Israel has rejected calls for an independent international investigation of its raids on the Gaza-bound aid flotilla on Monday that killed nine activists.

The raids have sparked international condemnation, with South Africa becoming the latest nation to withdraw its ambassador from Israel in protest.

Israel has defended the actions of its soldiers from the outset, saying the deaths of the activists onboard the humanitarian ships in international waters was an act of self-defence by its commandos.

Israeli government spokesman Mark Regev says his country holds itself to the highest international standards.

He says Israel's military will conduct the investigation into what happened.

"It is our standard practice that after all military operations - and especially operations where there have been fatalities - that we conduct a thorough, professional, independent investigation," he said.

But whether that is enough to satisfy the United States is not clear. The US had called for a "prompt, impartial, credible and transparent" investigation by Israel.

Yesterday US vice president Joe Biden suggested an Israeli probe with international involvement.

That was initially embraced by Israeli foreign minister Avigdor Lieberman, who said: "We have enough high-level legal experts - if they want to take on observers from the outside, they can invite observers."

Today, US president Barack Obama said he expected Israel to agree to an impartial investigation because they "recognise that this can't be good for Israel's long-term security".

But some EU countries are still demanding an international investigation and the Geneva-based UN Human Rights Council has decided to dispatch its own fact-finding mission.

That decision has been attacked by Israel's foreign ministry, which says the council has no moral authority and also said it was "working stubbornly against Israel".

All of this is against the backdrop of more ships determined the break the blockade.

The MV Rachel Corrie is motoring towards Gaza, carrying activists from Ireland and Malaysia. Among them is former United Nations humanitarian coordinator Dennis Halliday.

"This is a time for Israel to change its policy and to allow at least this small cargo boat into Gaza," he said.

"We are optimistic but we are also sanguine that this may not happen, that we will be boarded possibly by the Israelis.

"I suppose we have to anticipate they will do that in international waters, which again, would be a violation of international law."

That ship is expected to be intercepted but pressure is mounting on Israel to find a compromise on its blockade.

The Reuters newsagency says a plan under which the UN could search goods bound for Gaza during transit in Israel's Ashdod port was going to be discussed by Israeli prime minister Benjamin Netanyahu and his inner cabinet.

An international naval force is also being suggested.

An Israeli TV channel has reported the establishment of such a force to inspect ships bound for Gaza was discussed by Mr Netanyahu and former British prime minister Tony Blair.

Mr Blair is now the European Union's Middle East envoy. When speaking to reporters, he only discussed the situation in Gaza.

"I have been there calling for a change in policy on Gaza to open crossings for goods that should come into Gaza to help the people there for the best part of two years," he said.

"I don't think it is simply as a result of this incident. I just think the policy in Gaza is counterproductive and what we should be doing is allowing material in, that we build homes and sanitation and power and water systems."

The plight of Gaza's citizens has also been raised by Mr Obama.

While he acknowledged Israel's legitimate security concerns about Hamas, he said the blockade was preventing people from "pursuing economic opportunities".

Mr Obama says he hopes this week's tragic events could be used as an opportunity to advance the peace process.

He is due to meet Palestinian president Mahmoud Abbas at the White House on Wednesday.