"Had the Israeli government heeded to international calls and my own strong and urgent and persistent call to lift the blockade of Gaza, this would not have happened," Ban told Reuters in an interview on Tuesday in Kampala.

He was in Kampala to attend a review conference of the International Criminal Court (ICC).

In Brussels, Belgium, the North Atlantic Treaty Organization (NATO) is called for a "prompt, impartial, credible and transparent investigation" into the Israeli raid.

Representatives of the alliance's 28 nations met on Tuesday to discuss the incident. Secretary-General Anders Fogh Rasmussen demanded the immediate release of the detained civilians and ships held by Israel.

Turkey called the emergency meeting, but its representative did not demand that the alliance take collective action against Israel, said a diplomat who attended the talks. The official asked not to be named because of the sensitivity of the matter.

NATO, of which Turkey is a long-standing member, has reacted cautiously to the events. The alliance cooperates with Israel on anti-terrorism patrols in the Mediterranean.