The UN Security Council voted unanimously to protect humanitarian aid workers in war zones, despite some US misgivings over the wording of the resolution.

Mexico's draft version had referred to the International Criminal Court, before the United States demanded that the phrase be dropped.

The resolution was passed on Tuesday, a week after a bomb attack on the UN offices in Baghdad killed 23, including the UN envoy to Iraq, Sergio Vieira de Mello.

UN Secretary General Kofi Annan underlined the importance of a unanimous decision, in brief remarks ahead of the vote.

"Emphasising that there are existing prohibitions under international law against attacks knowingly and intentionally directed against personnel involved in a humanitarian assistance or peacekeeping mission undertaken in accordance with the Charter of the United Nations which, in situations of armed conflicts, constitute war crimes and recalling the need for states to end impunity for such criminal acts," the resolution said.

The United States objected to the original language that would have made any attack on humanitarian personnel a war crime, including acts committed in what it called the "fog of war."

US ambassador to the United Nations John Negroponte said: "This resolution creates no new international legal obligation but rather reaffirms existing regulation."

The US ambassador also recalled that other international conventions allow the occupying powers to restrict freedom of movement of aid workers in areas they control.

Annan emphasised that the resolution "strengthens the obligation to take every step to protect those working 'blue flag' and to bring to justice those who hurt them."

"It allows the governments to take action against the perpetrators and to work with us to be sure our personnel are not in harm's way."

He said that the removal of the mention of the ICC changed nothing.

"It was a compromise that was necessary to get the resolution passed," he said.

Non-governmental organisations and human groups lobbied for Mexico's draft resolution.