The statement said the investigation should be "prompt, impartial, credible and transparent".

It also condemned the "acts" which led to the deaths of at least 10 civilian activists during the operation.

The raid sparked strong international condemnation and calls for Israel to lift its three-year blockade of Gaza.

The UN statement was reached after hours of discussion as the council deliberated through the night.

Turkey is furious at the commando raid, which targeted a Turkish ship and appeared to have killed mostly Turkish activists, our correspondent says.

The compromise took out direct condemnation of Israel and removed references to an international investigation, our correspondent adds.

It also weakened demands for an end to the economic blockade of Gaza that the activists were trying to break, but the incident has refocused international attention on the siege and many states have renewed calls for it to be lifted, she says.

In its statement, the Security Council said it "deeply regretted the loss of life and injuries resulting from the use of force during the Israeli military operation in international waters against the convoy sailing to Gaza".

The Council "condemns those acts which resulted in the loss of at least 10 civilians and many wounded, and expresses its condolences to their families".

The Council requested the immediate release of the ships as well as the civilians held by Israel.

The Council also stressed that the situation in Gaza was "not sustainable".

Shortly after the statement was released, several Gaza militants crossed the border into Israel and exchanged fire with troops, the Israeli military said. Two militants were killed, it said.

'Self-defence'

Earlier, Turkey's foreign minister called Israel's actions "murder by a state".

Israel's UN envoy said troops acted in self-defence when activists attacked them, charges the campaigners deny.

He said the activists had used "knives, clubs and other weapons" to attack the soldiers who boarded the lead boat, the Mavi Marmara.

The campaigners insist the soldiers opened fire without any provocation.

Of the 679 surviving activists, who were brought to the Israeli port of Ashdod, only 50 agreed to be voluntarily deported and more than 30 are being treated in hospital for their injuries, reports the BBC's Wyre Davies in Jerusalem.

That means that almost 600 people, from several countries, are still being held in detention centres across Israel and are being questioned by the authorities.

Israel has imposed an information blackout, making it difficult to gather first-hand accounts from the campaigners.

The ships were carrying 10,000 tonnes of aid in an attempt to break Israel's three-year blockade of the Gaza Strip.

Israel says it will deliver the ships' aid cargo to Gaza by land.

The Israeli government is now engaged in a public relations battle trying to put across its version of events; it has released navy video pictures showing protesters on board the flotilla beating some of its officers, says the BBC's Jon Donnison in Gaza.

Later on Tuesday, Nato ambassadors will hold emergency talks at Turkey's request to discuss the raid.

Israeli Prime Minister Benjamin Netanyahu said he regretted any loss of life, but gave full backing to the action of the Israeli troops.

Mr Netanyahu cut short a visit to Canada to deal with the growing crisis and cancelled a scheduled meeting in Washington with US President Barack Obama on Tuesday. He is due back in Israel on Tuesday.

Israel tightened its blockade of the Gaza Strip after Hamas seized power there in 2007.

Israel says it allows about 15,000 tonnes of humanitarian aid into Gaza every week, but the UN says this is less than a quarter of what is needed.

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