(CNN) -- The European Union called Saturday for a "clear and strong" international response to the Bashar al-Assad regime's alleged use of chemical weapons in Syria, but said U.N. inspectors investigating the incident should report their initial findings before any action is taken.
The statement came as U.S. Secretary of State John Kerry sought to persuade skeptical European allies to join an international coalition on Syria after a Group of 20 summit ended Friday with a stalemate between Washington and Russia.
EU foreign policy chief Catherine Ashton read the statement, which she said reflected the position of all EU members, after four hours of talks Saturday between Kerry and EU foreign ministers in Vilnius, Lithuania.
"Information from a wide variety of sources confirm the existence of such an attack and seems to indicate strong evidence that the Syrian regime was responsible," it said, given that it was the only party with access to such weapons and the means to deliver them on such a wide scale.
The European Union called the use of chemical weapons a "blatant violation of international law, a war crime and a crime against humanity."
The statement did not explicitly endorse military action, but said the international community cannot remain idle and that "a clear and strong response is crucial to make clear that such crimes are unacceptable and that there can be no impunity."
At the same time, it said, the European Union underscores the need to address the Syrian crisis through the U.N. process. It hopes that U.N. chemical weapons inspectors who visited the site of the August 21 attack can report their preliminary findings as soon as possible.
It also welcomed comments by French President Francois Hollande that he would wait for the preliminary report before any military action was taken.
Kerry said he was grateful for what he called "a strong statement about the need for accountability."
The talks were expected to include "a fairly detailed discussion" of U.S. thinking on potential military action against Syria, senior State Department officials traveling with Kerry said ahead of the meeting. But the ministers would also discuss how to resolve the situation politically, they said.
Ex-Iran minister says he warned of sarin
Syria's government has blamed the chemical attack on opposition fighters, who it describes as terrorists with foreign backing.
Ali-Akbar Salehi, the former foreign minister of Iran, is reported by state news agency IRNA as saying that nine months ago, while he was still in office, he gave the Americans a letter through the Swiss Embassy in Tehran, warning them about the influx of chemical weapons such as sarin gas into Syria.
On Thursday, Britain announced that its military scientists found traces of sarin gas in soil and clothing taken from a patient treated near the site of the alleged August 21 attack. A day earlier, Kerry said that blood and hair samples from near the site "tested positive for signatures of sarin."
The United Nations has said more than 100,000 people -- including many civilians -- have been killed since a popular uprising spiraled into a civil war in 2011. An umbrella group for the rebels said 44 people were killed Saturday.
Syrian activist groups and state media reported heavy clashes in the ancient town of Maaloula, in the Damascus countryside.
The predominantly Christian town, an hour's drive from the capital, is the last surviving place where western Aramaic is spoken, and it holds huge symbolic importance for Syrian Christians.
Meanwhile, Kerry appeared alongside French Foreign Minister Laurent Fabius in Paris on Saturday, insisting, "This concerns every American's security. This is not remote. This not some far-off place where something happened that's just one Arab sect killing another Arab sect on some internal fight."
Kerry went on to liken al-Assad to Adolf Hitler and Saddam Hussein, citing the three men as the only leaders to deploy internationally banned chemical weapons in the last century. He further accused al-Assad of having "no conscience" about what he does to the Syrian people.
President Bill Clinton always regretted not addressing Rwanda before the African nation spiraled into all-out genocide in 1994, Kerry said the former president has told him, and if the United States doesn't confront Syria soon, it could face more severe manifestations of the threat later. The 1995 sarin attacks on the Tokyo subway are an example of what happens when "ungoverned terrorists call the shots," Kerry said.
Many European countries are opposed to any military action without a U.N. mandate, which the United States has ruled out over what it calls Russian "intransigence" in the U.N. Security Council.
France is the only nation so far to commit to military action against Syria alongside the United States.
Hollande has promised to contribute to a military campaign but, facing political pressure at home, said he would wait for the U.S. Congress to give President Barack Obama authorization to strike and for the findings of the U.N. inspectors' report, which would effectively delay any military action.
Kerry will also meet with Arab League foreign ministers Sunday while in Paris. Those talks initially were to focus on the latest Middle East peace initiative, but Syria is now expected to be on the agenda, the officials told reporters.
Kerry will talk to the Arabs "about things where they may be helpful, and again, also building support within the international community for a response from the international community," one of the officials said.
In all of the meetings Kerry was expected to work to "coordinate a political response" on Syria, but was not expected to go into the details about particular roles countries could play as part of any military action, an official said.
Kerry will also meet with UK Foreign Secretary William Hague in London. Britain's Parliament has ruled out getting militarily involved in Syria, but Prime Minister David Cameron has pledged to continue to push for a tough response against the Assad regime.
International opinion divided
Kerry's efforts with European allies paralleled those of his boss, Obama, who tried to rally members of the G20 in St. Petersburg, Russia.
Obama met with his Russian counterpart, Vladimir Putin, on the sidelines of the St. Petersburg summit Friday. But despite both saying the talks were constructive, there was no sign of consensus.
International opinion remains divided on what should be done after the Syrian government allegedly used chemical weapons against its own people last month.
A statement issued Friday by a bare majority of the G-20 -- 11 of its 20 members -- said that "the evidence clearly points to the Syrian government being responsible for the attack, which is part of a pattern of chemical weapons use by the regime."
"Those who perpetrated these crimes must be held accountable," it said.
The statement called for a "strong international response" and "supports efforts undertaken by the United States and other countries to reinforce the prohibition on the use of chemical weapons." It did not expressly endorse military action, although U.S. officials said the nations who signed it interpreted the statement as tacit support for strikes.
German Foreign Minister Guido Westerwelle also signed on to the statement Saturday.
Obama has stressed he is considering a limited and targeted mission to respond to the use of chemical weapons and deter the Assad regime from using them again, a point stressed in more than eight hours of testimony on Capitol Hill this week by Kerry, Secretary of Defense Chuck Hagel and Martin Dempsey, chairman of the Joint Chiefs of Staff.
Obama described his exchange with Putin in St. Petersburg as "candid" -- but acknowledged that the Russian president was unlikely to support his call for military action against Syria.
Putin gave reporters a similar account, adding, "He doesn't agree with me, I don't agree with him, but we listened to each other."
Both leaders said they could work together to seek a political solution to the Syrian crisis.
The two men hold opposing views over whether military action should be taken against the Syrian government.
Obama said the world must act to uphold an international ban on chemical weapons use, while Putin repeated the Syrian government's accusation that "militants" used chemical weapons in a bid to get aid and support from "those countries who support them."
He told reporters that Moscow will continue to provide Syria with arms and humanitarian aid. Russia, along with China, has so far opposed military intervention in Syria at the U.N. Security Council.
Obama's domestic battle
Obama will now seek to rally congressional support for possible U.S. military action against Syria, with a vote expected after lawmakers reconvene from recess on Monday.
The president will give interviews with CNN, PBS, Fox, NBC, ABC and CBS on Monday as he presses his case, a White House official said; the CNN interview will air at 6 p.m. The next day, he'll address the American people on this crisis.
Obama said Friday that he had expected skepticism from the public and from lawmakers, and that he had anticipated it would be "a heavy lift" to win approval for military action from Congress.
In Paris, Kerry spoke of Americans' "Iraq hangover" and said, "We all got burned by that, and we're still paying the price."
The United States, however, can't allow their tentativeness about Iraq strip away the nation's responsibility "to confront real threats today," he said.
Even as Kerry has led calls within the administration for tougher action against Syria, he has sought to work with Russian Foreign Minister Sergei Lavrov on bringing the warring parties in Syria together for negotiations on a political transition.
A senior State Department official said Kerry would be discussing those efforts during his meetings this weekend, although no date has been set yet and the parties have "some distance to go" before the talks could be held.
The United States hopes military action, however limited, could change Al-Assad's calculus and encourage him to negotiate.
Middle East peace process
Although Syria is sure to top the agenda during Kerry's meetings with foreign diplomats, he will also discuss his efforts to nurture the fledgling Middle East peace process.
After five months of shuttle diplomacy between Israelis and Palestinians, Kerry in July announced a resumption of direct talks between the two sides and tapped former U.S. Ambassador to Israel Martin Indyk as his Mideast peace envoy.
The parties have committed to try and reach a peace deal within nine months, although privately both sides have voiced skepticism that that is possible.
Kerry will meet in London on Sunday with Palestinian President Mahmoud Abbas. Another senior State Department official traveling with Kerry said that although the crises in both Syria and Egypt have distracted both the Israelis and Palestinians, they have also yielded important benefits.
Kerry was also expected to lobby EU foreign ministers to reconsider sanctions imposed this summer against Israel, which banned funding of some projects in the occupied West Bank over European opposition to continued settlement building.
CNN's Elise Labott wrote and reported from Vilnius and Laura Smith-Spark from London. CNN's Eliott C. McLaughlin, Nic Robertson, Neda Farshbaf and Bharati Naik contributed to this report.