An Israeli helicopter missile strike on a car in Gaza City killed top Hamas leader Abdel-Aziz Al Rantissi last night. Two of his bodyguards were also killed when two missiles were fired. Al Rantissi, 56, Hamas leader in the Palestinian group's Gaza Strip stronghold, had been rushed to a Gaza City hospital in critical condition after he had been wounded in the head with shrapnel. Hundreds of Hamas members and supporters rushed to the hospital after news of the Israeli raid. A crowd of Palestinians also swarmed around the wreckage of the white car, pulling out what appeared to be fragments of clothing. Hamas issued an immediate vow of revenge. "Israel will regret this. Revenge is coming," senior leader Ismail Haniya said. "This blood will not be wasted. It is our fate in Hamas and it is our fate as Palestinians to die as martyrs. The battle will not weaken our determination or break our will," he said. Al Rantissi, a co-founder of Hamas, had become one of its two main leaders since Israel's killing of Hamas spiritual head Ahmed Yassin in Gaza on March 22. The air strike came hours after an Israeli border policeman was killed by a Palestinian bomber at the main Erez crossing on the Israeli-Gaza border. Last June, Al Rantissi and his teenage son were wounded in an Israeli helicopter missile strike on his car. Palestinian President Yasser Arafat "vigorously condemned" Al Rantissi's assassination. British Foreign Secretary Jack Straw condemned the assassination as unlawful. "The British Government has made it repeatedly clear that so-called targeted assassinations of this kind are unlawful, unjustified and counterproductive," he said. The United States refrained from condemning the killing of a top Hamas leader on Saturday and limited its criticism of the assassination to saying it feared for the stability of the Middle East. Al Rantissi's car was hit by two missiles about a block from his house in the Sheikh Radwan neighbourhood of Gaza City. "I heard the sound of the explosion. It was a small one followed after less than two seconds by another one," said Rawhi Ghazal, 35, who owns a nearby shop. Al Rantissi ran about 15 metres from the car, collapsed and lost consciousness, Ghazal said. The Hamas leader, his body pocked with bloody wounds and blood streaming from his head and neck, was rushed to the hospital. **PHOTO CAPTION*** Sheikh Ahmed Yassin, left, and Abdel Aziz Rantisi, are seen during a meeting at Yassin's house in Gaza City, in July 9, 2003 file photo. (AP)