Israel's defence minister has expressed regret for the deaths of pro-Palestinian activists in a clash with navy commandos. But he has blamed the violence on organisers of a flotilla carrying aid to the blockaded Gaza Strip. Speaking at a news conference in Tel Aviv, Ehud Barak called the aid flotilla a "political provocation" by anti-Israel forces. He said the sponsors of the flotilla are violent. Israel's military chief, Lt Gen Gabi Ashkenazi, said soldiers were forced by violent activists to respond with live fire. More than 10 pro-Palestinian activists were killed after attacking naval commandos who were halting the "Freedom Flotilla" heading toward the blockaded Gaza Strip, according to the Israeli army. The army said the soldiers were attacked with knives and clubs as they boarded the six vessels. The violence turned deadly after one of the activists grabbed a weapon from one of the commandos, the army said. The weapon discharged, though it was not clear whether the activist fired it or if it went off accidentally. Dozens of people were wounded, both soldiers and activists. Israeli Arab groups say a prominent activist is among the wounded. Unconfirmed media reports from Hamas' Al Aqsa television said up to 20 passengers had been killed, of whom nine were Turkish nationals. Israel's security forces were placed on high alert to handle any on high "possible disturbances" and the military censor blocked the reporting of any information about people killed or injured and transferred to Israeli hospitals after the incident. Israel expressed its "sorrow" over those killed, an Israeli cabinet minister said. "I can only express my sorrow over all the deaths," the industry and trade minister Binyamin Ben Eliezer told army radio by phone from Doha where he is attending the World Economic Forum. Israeli prime minister Benjamin Netanyahu would stay in Canada and not return home in the wake of a deadly navy raid, a senior official with the delegation said. "The prime minister is not leaving, he will carry on with his schedule," the official told reporters in Ottawa. An AFP correspondent travelling with the delegation said the situation was one of "complete confusion." "First were were ordered to pack, then we were told to put everything on hold," he said, adding that an official had said members of the delegation were currently "in consultations." Earlier, Israel public radio had reported that Mr Netanyahu was to cut short his trip to return home in the wake of a deadly pre-dawn raid by the Israeli navy. The Israeli leader is due to visit the White House on Tuesday for talks with US President Barack Obama, aimed at mending ties between the two allies which have been strained due to a spat over Jewish settlements. Meanwhile, the Palestinian president Mahmud Abbas slammed the raid as "a massacre". "We consider this to be a massacre and we condemn it," an official from Abbas' office said on Palestinian television, announcing a three-day mourning period. "We will have to take some difficult decisions this evening." Hamas immediately urged Arabs and Muslims to "rise up" in front of Israeli embassies across the globe in protest against the raid on the fleet of aid ships, among them Turkish vessels. "We call on all Arabs and Muslims to rise up in front of Zionist embassies across the whole world," said a Hamas spokesman Sami Abu Zuhri, using the Arabic word 'intifada'. Ismail Haniya, the Islamist movement's prime minister in Gaza, slammed the "ugly attack" in a statement in which he called for "the United Nations to protect the activists" on board the boats. Arab League chief Amr Mussa slammed the raid as a "crime" against a humanitarian mission. "We condemn this crime, taken against a humanitarian mission and people. They were trying to help people. They were not on a military mission. Everyone should condemn this," Mr Mussa said. "We are now conducting calls to Arabs to decide on our next step," said Mr Mussa, who heads the 22-country organisation based in Cairo. The Israeli ambassador was summoned to the Turkish foreign ministry in response to the raid, a Turkish diplomat said. "The ambassador (Gabby Levy) was summoned to the foreign ministry. We will convey our reaction in the strongest terms," the diplomat, who asked not to be named, said. The deputy prime minister Bulent Arinc meanwhile conveyed an emergency meeting with senior officials, including the minister of the interior, the navy chief and the army's head of operations, Anatolia news agency reported. Mr Arinc was in charge as prime minister Recep Tayyip Erdogan is currently on a visit to Chile. Turkish police blocked dozens of stone-throwing protesters who tried to storm the Israeli Consulate in Istanbul. CNN-Turk and NTV showed dozens of angry protesters scuffling with Turkish police guarding the consulate in downtown Istanbul. "Damn Israel," the protesters shouted. Protesters later staged a more peaceful demonstration outside the consulate, holding up Palestinian flags and listening to readings from the Qoran. Activists also start gathered outside the Israeli ambassador's residence in the Turkish capital. Two TV networks reported earlier that Israeli warships attacked the six ships carrying pro-Palestinian activists and aid for blockaded Gaza. "We were not expecting such an operation in international waters," Omer Faruk Korkmaz, an official of the pro-Islamic aid group, IHH, that led the aid shipment said in Turkey. "Israel has been caught red-handed and the international community will not forgive it." Mr Korkmaz said the ship was being escorted to Haifa. "I was expecting an intervention," said Murat Mercan, a lawmaker from the prime minister's ruling party. "I was not expecting bloodshed, the use of arms and bullets. Israel is engaged in activity that will extremely hurt its image," he said. The attack may lead to "irreparable consequences" in bilateral ties, Turkey's foreign ministry said. "By targeting civilians, Israel has once again shown its disregard for human life and peaceful initiatives. We strongly condemn these inhumane practices of Israel," a written statement said. "This deplorable incident, which took place in open seas and constitutes a fragrant breach of international law, may lead to irreparable consequences in our bilateral relations," it said. "Whatever the reason is, such action against civilians involved only in peaceful activities is unacceptable. "Israel will have to bear the consequences of this behaviour, which constitutes a violation of international law," it said. WAM, the state news agency, reported that the Palestinian ambassador to the UAE, Dr Khairi al Oridi, had slammed the Israeli attack on the relief vessel. WAM said that he described the attack on the fleet and killing of the activists as a criminal, despicable, irresponsible act that depicts the aggression course of the Israeli government against humanity. Dr Oridi underlined that the international silence allows the Israeli government to commit more atrocities and violence, indicating that the lack of the international community's will to check the Israeli acts encourages them to continue committing more crimes, WAM added. EU foreign affairs chief Catherine Ashton demanded Israeli authorities mount a "full inquiry" into the deaths. Ms Ashton "extends her sympathies to the familes of the dead and wounded and is demanding a full inquiry into the circumstances of how this event happened," said a spokesman. "She reiterates the European Union's position regarding Gaza - the continued policy of closure is unacceptable and politically counterproductive." Greece also summoned Israel's ambassador to demand an "immediate" report on the safety of about 30 Greeks on board the aid ship flotilla. The foreign ministry said in a statement it had requested "immediate information concerning the safety of Greek citizens on board the boats ... and stressed the need to take the necessary measures to ensure their security". Ambassador Ali Yahya was called in for talks with the Greek deputy foreign minister Dimitris Droutsas. The Vatican voiced "deep sadness" over the Israeli raid on the flotilla. The Holy See feels "deep sadness and concern" over the pre-dawn storming of the aid flotilla in which up to 19 pro-Palestinian activists were killed, a Vatican spokesman Federico Lombardi said.