Washington (CNN) -- The United States on Thursday will call for Syrian President Bashar al-Assad to step down, senior U.S. officials tell CNN.
The White House was expected to release a statement confirming the move, followed by a formal announcement Thursday morning by Secretary of State Hillary Clinton.
The move has been closely coordinated with European, Turkish and Arab allies and would come one day after al-Assad told the head of the United Nations that military and police operations against anti-government protesters have stopped, according to a statement released by the Secretary-General's office.
U.S. officials, who asked not to be named because of the sensitivity of the matter, said they expect similar calls for al-Assad to step down in coming days for other leaders.
Senior U.S. officials, diplomats and members of the Syrian opposition point to the next several weeks as a critical timeframe for increasing al-Assad's diplomatic isolation, strengthening sanctions against the regime and for the opposition to announce measures aimed at unifying and streamlining their activities, both inside and outside Syria.
The campaign against al-Assad, which involves intense diplomatic outreach by Secretary of State Hillary Clinton and even President Barack Obama himself, is modeled after the one the United States used in Libya, where the Obama administration built international consensus for the NATO mission to protect civilians.
Although nobody is talking about military intervention in Syria, Clinton and Obama have been working with European, Turkish and Saudi leaders to coordinate tougher diplomatic and economic action against al-Assad.On Tuesday, Clinton said the brutality against the Syrian people is "galvanizing international opinion" against the regime.
"I happen to think where we are is where we need to be, where it is a growing international chorus of condemnation," Clinton said earlier this week during a joint interview with Defense Secretary Leon Panetta at National Defense University.
She said America was "putting together a very careful set of actions and statements that will make our views very clear."
On Thursday, the Security Council will hold consultations on Syria, when they will be briefed by U.N. High Commissioner for Human Rights Navi Pillay.
Officials said Pillay is expected to give a sober assessment of the situation on the ground in Syria.
France and other European countries are continuing to push for a Security Council resolution condemning the al-Assad regime, but they are still facing stiff resistance from Russia, China, Brazil, India and South Africa. The United States is pushing for special session on Syria at the U.N. Human Rights Council in Geneva, Switzerland, as early as next week.
Diplomats say they hope Pillay's briefing on Thursday will generate momentum for further action, including widespread calls for al-Assad to step down over the coming days and build consensus toward the Security Council resolution, which could serve as a pretext for further action.
The United States has faced increased pressure to call on al-Assad to step down.
Although the Obama administration has said al-Assad has "lost legitimacy" and Syria "would be better off" without him, U.S. officials have resisted calling explicitly for his ouster.
Clinton noted that because the United States has a rocky relationship with Syria, such a message would have more resonance coming from voices in the region, which she called "essential" for there to be impact inside the country.
"We want a bunch of people singing out of the same hymn book," Clinton said. "It's not going to be any news if the United States says, 'al-Assad needs to go.' Okay, fine. What's next? If Turkey says it, if (Saudi) King Abdullah says it, if other people say it, there is no way the Assad regime can ignore it," Clinton said.
Senior American officials cite increased brutality in the town of Hama during the holy Muslim month of Ramadan as galvanizing global opinion toward the belief that al-Assad has no intention of stopping the violence. One senior official said the United States is "trying to absorb the international outrage and turn it into action."
"We are trying to put wings under these countries sentiments," the official said. "al-Assad is providing by his action he isn't caring and we are saying, 'if you are so morally outraged, put some action behind it, including your trading relationships, rhetoric and supporting action at the U.N.'"
While nobody expects al-Assad to stop the violence because of the measures, senior U.S. official say the series of coordinated tough diplomatic action is meant to send a message of encouragement to the opposition, as well as possibly inspire members of the regime to abandon al-Assad.
"It's also meant as a message to other leaders to demonstrate that if they continue to use violence, there will be consequences," another senior U.S. official said.
Clinton said Tuesday the administration was pushing for "stronger sanctions that we hope will be joined by other countries that have far bigger stakes economically than we do." Congress is currently preparing a bill authorizing the Obama administration to impose sanctions against Syrian oil and gas sectors, which senior U.S. officials have said are being readied.
On Tuesday, a group of Syrian activists and energy experts met with administration officials, where they presented an assessment on the impact possible sanctions against Syrian oil and gas sectors would have on the regime.
The European Union, which has a much greater investment in those sectors, is also working on similar measures which could have far greater impact on the regime. Clinton also urged countries like China and India, to stop buying Syrian oil and gas and has urged Russian leaders to stop selling arms to Damascus.
For months Turkey has been urging Syria to stop the violence and implement reforms. Last week Turkish Foreign Minister Ahmet Davutoglu traveled to Damascus for meetings with Assad, who promised to implement reforms, only to intensify the crackdown days later.
On Wednesday Turkish Prime Minister Recep Tayyip Erdogan signaled Turkish patience with Syria was running out, comparing the situation to the one in Libya, where Turkish efforts to mediate were unsuccessful.
"We have done our best on Libya, but haven't been able to generate any results. So it's an international issue now. Gaddafi could not meet our expectations, and the outcome was obvious," Erdogan told reporters in Istanbul.
"Now the same situation is going on in Syria. I've sent my foreign minister, and personally got in touch many times, the last of them three days ago on the phone. In spite of all this, civilians are still getting killed."
Senior U.S. officials say that while Turkey has held out on completely abandoning Syria, the increased brutality during Ramadan -- even in the face of Turkish demands to stop -- seems to be bringing Ankara to the view that Assad has lost legitimacy.
The officials said that while Turkey may be reluctant to support sanctions, Ankara may now be willing to support tougher diplomatic action, including joining calls for Assad to step down.
"They have been reluctant to give up on what they saw as a special relationship," one senior U.S. official said.
"They have gone from seeing Assad as a brother and a friend, to someone they have questions about, to someone who concerns them. They haven't wanted to cross the threshold of entirely giving up any hope for the regime to reform but I think they are there."
Saudi Arabia has also called on al-Assad to stop what King Abdullah called the "killing machine" and is urging Arab nations to speak out against al-Assad's brutality against his people.
The king, who spoke last week with Obama, recalled the Saudi Ambassador from Damascus. Bahrain, Kuwait and Tunisia have already followed suit.
Similarly, several Arab League countries, including all Gulf countries and Jordan, have publicly condemned the violence.
The move to tighten the noose against the al-Assad regime comes as the Syrian opposition has been taking steps to better organize their efforts.
Members of the opposition say Syria's disparate groups are working toward a unified front that includes classic opposition figures from all sects and backgrounds as well as representation from the two main opposition groups, the Local Coordination Committee (LCC) and the Syrian Revolution Coordination Union (SRCU).