Israel's allies froze military ties and summoned its ambassadors today over the storming of a aid flotilla bound for Gaza, as Muslim leaders slammed the deadly raid as "criminal" and "inhuman".

Up to 19 people are believed to have been killed.

UN Secretary General Ban Ki-moon said he was "shocked" by the deadly Israeli assault on a convoy carrying hundreds of pro-Palestinian activists, lawmakers and journalists through international waters towards besieged Gaza.

"It is vital that there is a full investigation to determine exactly how this bloodshed took place," Ban said, calling on Israel to "urgently" explain itself over the raid, which left up to 19 dead, many of them reportedly Turks.

As the Vatican voiced "deep sadness and concern" at the loss of life, capitals across Europe summoned Israel's ambassadors to explain the assault.

Ankara responded with fury, recalling its ambassador from Tel Aviv and warning the assault would have "irreparable consequences" to bilateral ties.

Police held back angry crowds shouting "Damn Israel" outside Israel's missions to the country, as Turkey accused Israel of a "fragrant breach of international law," and "disregard for human life and peaceful initiatives."

Deputy Prime Minister Bulent Arinc also said plans for three joint military exercises with Israel had been scrapped.

Greece, which had dozens of nationals in the convoy, pulled out of joint military exercises with Israel and cancelled a visit by its air force chief, as an aid group claimed that commandos in helicopters had fired on a Greek vessel.

Israel said its naval forces were attacked after they stormed six ships loaded with thousands of tonnes of aid and with hundreds of activists aboard, and that both sides used live fire.

But Iran's President Mahmoud Ahmadinejad denounced the raid as "inhuman Zionist regime action," while the Islamist movement Hamas which rules Gaza urged world Muslims to "rise up" in protest.

Palestinian president Mahmud Abbas declared three days of mourning over the "massacre," while Arab League chief Amr Mussa called it a "crime."

Lebanese Prime Minister Saad Hariri called for an emergency meeting of the UN Security Council, which his country currently chairs, a government official said.

Egypt condemned the "acts of killing committed by Israel forces" while Kuwait's parliament speaker said the storming of the flotilla, which was carrying 16 Kuwaitis including an MP, was a "heinous Israeli crime."

In Europe, condemnation was equally swift.

The European Union foreign affairs chief Catherine Ashton demanded Israel mount a "full inquiry," as member states ordered an emergency meeting of their ambassadors to the EU in Brussels on Monday.

Spain -- the current European Union president -- France, Sweden, Norway, Denmark, Austria and Greece summoned Israel's ambassadors for explanations, with Madrid slamming the operation as "unacceptable".

France's President Nicolas Sarkozy accused Israel of a "disproportionate use of force" while Foreign Minister Bernard Kouchner insisted "nothing can justify" such violence.

Germany's Foreign Minister Guido Westerwelle also said he was "deeply concerned" about the deaths, while Italy's Foreign Minister Franco Frattini "deplored" the loss of civilian life.

Israel's Channel 10 TV said 19 passengers were killed and 36 wounded in the raid.

The bloody ending to the high-profile mission to deliver supplies to Gaza came on the eve of a meeting in Washington between President Barack Obama and Israeli Prime Minister Benjamin Netanyahu.

Thousands of Palestinian refugees and activists demonstrated across Lebanon to denounce the raid, some chanting slogans like "Give us weapons, give us weapons and send us on to Gaza."

Maen Bashur, a Lebanese coordinator for the mission, said activists had expected the convoy to be "attacked" by the Israelis and considered those seized on board the ship as "war prisoners".

A Cyprus MEP Kyriacos Triantafyllides, who was prevented at the last minute from joining the aid mission, told the Cypriot news agency CNA that activists had "expected a strong reaction from Israel."

"But nobody believed it would come to this point where they would face something akin to an invading army," he said.