The US embassy in Israel has advised its citizens to leave the Gaza Strip after a bomb attack on a convoy of American diplomatic vehicles killed three Americans and wounded a fourth person.

Washington has vowed to hunt down those responsible for the attack. The convoy had just crossed into Gaza from Israel when the attack took place. It was carrying US diplomats observing the implementation of the so-called road map peace plan.

Separately,the European Union has demanded that the Palestinian President Yasser Arafat takes swift action to hunt down the perpetrators of the attack.

Palestinian sources have said Israeli forces backed by combat helicopters have began an incursion into the northern Gaza Strip following the attack.