BRUSSELS (AFP) – Israel found itself isolated on the global stage Tuesday as world leaders demanded a swift and honest investigation into its deadly commando raid on a Gaza-bound humanitarian aid flotilla.

A day after the pre-dawn assault in international waters which left nine pro-Palestinian activists dead, nations across the world condemned the Jewish state for what Turkey's prime minister branded "a bloody massacre."

In New York, an emergency session of the UN Security Council called for "a prompt, impartial, credible and transparent investigation" that would satisfy international standards.

It also demanded the immediate release of all six vessels and the hundreds of Palestinian supporters who were on board.

Most of those killed in the violence were Turkish and Prime Minister Recep Tayyip Erdogan said Israel should be "punished."

"The insolent, irresponsible and impudent attack by Israel, which went against law and trampled human honour underfoot, must definitely be punished," he told lawmakers from his ruling party.

Turkey, once Israel's main partner in the region, has scrapped joint war games and recalled its ambassador.

Britain, France, Russia and China, four of the five veto-wielding Security Council members, urged Israel to lift its blockade of the Gaza Strip.

Even the United States, traditionally Israel's strongest ally, hinted that the blockade -- in place since 2007, when the Islamist Hamas movement seized control of the territory -- should at least be eased.

The outrage that greeted the raid prompted Israeli Prime Minister Benjamin Netanyahu to call off a visit to Washington and talks with US President Barack Obama.

The White House voiced "deep regret" at the loss of life and said it was waiting for the full facts to emerge, but also made it clear that it trusted Israel to carry out a full and credible investigation.

"Ultimately, this incident underscores the need to move ahead quickly with negotiations that can lead to a comprehensive peace in the region," it added.

Meanwhile delegates from the European Union and NATO gathered in Brussels for talks, after EU ambassadors criticised Israel's use of force and demanded an immediate and impartial inquiry.

Russia, hosting a summit in Rostov-on-Don with the European Union, backed the call for a probe, with President Dmitry Medvedev slamming the loss of life as "absolutely unjustified."

EU president Herman Van Rompuy said the deaths were "inexplicable."

China said it was "shocked" by Israel's actions and was prepared to back a quick response from the UN Security Council.

In Geneva, the 47-member UN Human Rights Council was due to hold a special session to consider setting up an international fact-finding mission.

UN chief Ban Ki-moon said he was "shocked" by the naval assault and called for Israel to "urgently" explain itself.

Across the world, tens of thousands of people protested on the streets and many countries summoned Israel's ambassadors.

Israel had warned that it would intercept the ships, but Monday's assault turned into a fiasco. Live footage from one vessel showed black-clad commandos clashing with activists and several wounded people lying on the deck.

The Israeli military, which blamed activists on the ship for creating the confrontation by attacking its soldiers as they boarded, said nine passengers were killed in the fracas.

The Muslim world united in condemning what Palestinian leader Mahmud Abbas called a "massacre" and Arab League chief Amr Mussa said was a "crime."

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

Egyptian President Hosni Mubarak condemned the "excessive and unjustified force" while Jordan, the only regional power other than Cairo to have a peace treaty with Israel, handed in a protest note.

The pan-Islamic Organisation of the Islamic Conference called on Israel to release all the boats and activists and take action against those responsible for the raid.