Turkish Prime Minister Tayyip Erdogan on Monday accused Israel of state terrorism after Israeli marines stormed a Turkish aid ship bound for Gaza.
"This action, totally contrary to the principles of international law, is inhumane state terrorism. Nobody should think we will keep quiet in the face of this," Erdogan told reporters from Chile, where he was cutting short an official visit to Latin America to deal with the crisis.
The raid, in which at least 10 pro-Palestinian activists were killed, triggered a diplomatic crisis and plans for an emergency session of the UN Security Council.
European nations, as well as the United Nations and Turkey, voiced outrage at the bloody end to the bid to break Israel's blockade of the Gaza Strip.
Its navy stopped six ships ferrying 700 people and 10,000 tons of supplies toward the Islamist-run Palestinian enclave.
In Washington, Israel's powerful friend the United States said only that it regretted the loss of life and was looking into the "tragedy".
Israeli Prime Minister Benjamin Netanyahu, who was in Canada and expressed full support for the navy operation, cut short a visit to North America that was to have ended on Tuesday with a meeting at the White House with US President Barack Obama.
As the captured foreign vessels were escorted into Israel's port of Ashdod, accounts were sketchy of the pre-dawn operation, some 120 km (75 miles) out in the Mediterranean. Marines stormed aboard from dinghies and rappelled down from helicopters.
Senior Israeli defense officials said at least 10 civilians died on the Mavi Marmara, a Turkish cruise ship carrying 581 people, after commandos came under fire, including with weapons that the activists had snatched from the boarding party. Seven of the troops and 20 protesters were injured, the military said.
German Chancellor Angela Merkel spoke with both Netanyahu and Erdogan in an effort to ease tensions. "We must make every effort to avoid escalation, and therefore everything must be clarified as soon as possible," she said, adding that the presence of international observers "can assist the investigation" into the raid.
Irish Prime Minister Taoiseach Brian Cowen called for an international inquiry into the Israeli raid, and expressed concern for the 10 of Irish nationals who took part in the sail.
Cowen said he believed Israel’s blockade of humanitarian assistance to Gaza was illegal under international law.
“Whilst the Israeli government has withdrawn from Gaza, they remain a de facto occupying force since they decide what gets into Gaza and who gets out of it,” he told the Irish Times.
Yael Branovsky contributed to this report