(CNN) -- International leaders expressed shock and dismay Monday over the Israeli navy's pre-dawn storming of a flotilla of ships carrying humanitarian aid for Gaza that resulted in nine deaths.
The situation rapidly escalated from a deadly incident at sea to a major diplomatic international crisis.
"I condemn the violence, and Israel must explain," United Nations Secretary-General Ban Ki-moon said in Uganda after the official opening of the International Criminal Court Review Conference.
In New York, the Security Council met in emergency session to discuss the matter.
The Israeli Foreign Ministry said the flotilla was trying to circumvent Israel's naval blockade of Gaza and defended its move as justified.
"This happened after numerous warnings from Israel and the Israel navy that were issued prior to the action," it said on its website. "During the interception of the ships, the demonstrators on board attacked the [Israel Defense Forces] naval personnel with live fire and light weaponry including knives and clubs."
But Palestinian Prime Minister Salam Fayyad said there was no excuse for an attack "by armed forces on a humanitarian convoy."
"The Palestinian government strongly condemns this crime, which portrays, once again, Israeli disrespect for the lives of innocent civilians, and its disrespect for international law," Fayyad said.
Palestinian President Mahmoud Abbas called for three days of mourning in the Palestinian territories, while Saeb Erakat, the chief Palestinian negotiator, said the attack was "on civilians who came from all over the world peacefully with wheelchairs and food supplies and medical supplies."
International response was overwhelmingly critical. Sami Abu Zuhri, a spokesman for Hamas, said: "The Israeli occupation tries to deny this massacre by saying that the activists on the boat are from Hamas and Muslim Brotherhood and this is a lying campaign, because the activists are international activists."
The U.N. urged Israel to take no further steps that could endanger civilian lives.
"We wish to make clear that such tragedies are entirely avoidable if Israel heeds the repeated calls of the international community to end its counterproductive and unacceptable blockade of Gaza," said a joint statement from Robert Serry, U.N. special coordinator for the Middle East peace process, and Filippo Grandi, commissioner general of the U.N. Relief and Works Agency.
White House Spokesman Bill Burton said the United States "deeply regrets the loss of life and injuries sustained and is currently working to understand the circumstances surrounding this tragedy."
That did not impress Namik Tan, the Turkish ambassador to the United States, who called the U.S. response "sort of weak."
Tan called the attack "unacceptable" and an "act of piracy" and said he "expects a strong reaction from the United States."
Asked what Turkey wants the United States to do on any potential statement or censure from the Security Council, the ambassador said the question was too "hypothetical."
He added, however, "Israel should not get away with this."
Turkey has long been Israel's only real Muslim friend in the Middle East.
In Istanbul, demonstrators tried to storm the high-rise building in which the Israeli Consulate is located. "Zionist dogs!" some chanted.
Moscow condemned the action as a "gross" violation of international law, according to the Interfax news agency. "Condemnation and deep anxiety are being expressed in Moscow, primarily in view of the fact that some of the participants in the humanitarian convoy were killed or injured," the Foreign Ministry said in a news release, according to Interfax.
Egyptian President Hosni Mubarak condemned Israel's use of force as "excessive and unjustified."
Former Prime Minister Tony Blair, an envoy to the Middle East on behalf of the so-called Quartet, a group of nations working toward peace in the region, called for a "full investigation" and said in a statement: "I repeat my view that we need a different and better way of helping the people of Gaza and avoiding the hardship and tragedy that is inherent in the present situation."
A number of nations, including Italy, France, Greece and Sweden, summoned their ambassadors to explain.
According to CNN Swedish affiliate TV4, 11 Swedes were among the activists aboard the ships. In addition, three members of Germany's Die Linke party were among those on the boat where nine people were killed, the party said Monday.
German Foreign Minister Guido Westerwelle called for a "thorough and transparent investigation" and called for border crossings to be opened to humanitarian aid convoys.
"I hope that the tragic events of last night will not make even more difficult the indirect talks between Israelis and Palestinians which have begun," he said. "We believe it vital that this process go forward."
Norway's Prime Minister Jens Stoltenberg said Norwegian citizens were aboard the convoy and called for an independent international inquiry "as soon as possible."
After meeting with the Israeli ambassador, the Greek Foreign Ministry said that the visit of the Israeli Joint Chiefs -- scheduled for Tuesday -- was being postponed and that the Greek-Israeli military exercise that was in progress had been discontinued.
A Greek Foreign Affairs Ministry official could not say how many Greeks were aboard the six ships in the flotilla.
Turkey recalled its ambassador from Israel, canceled three military exercises with the Israeli military and called home its youth national football team, which had two games scheduled in Israel, said Deputy Prime Minister Bulent Arinc.
"This operation will leave a bloody stain on the history of humanity," he said. Protests occurred Monday outside the Israeli Embassy in Istanbul, Turkey.
Lebanese Prime Minister Saad Hariri predicted that the raid would inflame the region.
"Lebanon strongly condemns this attack and calls on the international community, and specifically on the major countries which are supposed to be responsible about the peace process, to take action in order to stop this continuous violation of human rights, which is putting the international peace at risk," Hariri said.
Pakistan said it was concerned about the well-being and whereabouts of two journalists who were aboard the flotilla.
"The government of Pakistan strongly condemns the use of brazen force by Israel against a humanitarian mission that was embarked on delivering humanitarian aid to the Palestinian people in Gaza," the country's foreign ministry said.
"The killing of members of this humanitarian mission, which also included women, is brutal, inhuman and constitutes a flagrant violation of international law and norms."
In a statement on its website, the Kingdom of Bahrain said it "strongly condemns the Israeli navy's barbaric attack."
The Vatican said it was following the situation "with great attention and concern."