United States vice president Joe Biden has backed Israel's right to board ships bound for Gaza to prevent weapons smuggling.
Three planes carrying 466 activists from the Gaza-bound aid flotilla intercepted by Israeli forces have arrived in Istanbul from Israel.
The planes also flew back the bodies of nine activists killed when Israeli commandos took control of the six aid vessels trying to break Israel's blockade of Gaza.
Mr Biden says the US remains concerned about the plight of Palestinians in the Gaza Strip.
He says the needs to put pressure on Israel to allow in aid shipments such as building materials.
However, he says Israel has an absolute right to deal with its security interest and to stop weapons getting into Gaza.
The United States has not joined the international condemnation of Israel's use of force.
United Nations secretary-general Ban-Ki Moon has demanded that Israel immediately lift its blockade of the Gaza Strip.
Mr Ban called the blockade counter-productive, unsustainable and wrong.
The blockade was established after Hamas won power in Gaza in 2007.
Israel rejects demands
Israeli prime minister Benjamin Netanyahu has defended the deadly raid on the aid convoy.
Mr Netanyahu says Israel will continue to blockade the Gaza Strip.
He says to lift the embargo would turn the Hamas-run Palestinian enclave into a base for Iranian missiles that would threaten both Israel and Europe.