The Israeli strike brought warnings to both sides from Washington of the danger of a new cycle of violence and prompted the Islamic militant group to abandon the ceasefire. It came after fresh sweeps into several West Bank towns by Israeli forces early yesterday to hunt down known militants.

Reflecting American concern that the latest peace plan might be beyond repair, Colin Powell, the US Secretary of State, told both sides that they faced falling off a precipice and into yet another round of tit-for-tat violence.

“The end of the road map is a cliff that both sides will fall off,” he said during a visit to the United Nations in New York. He appealed to Yassir Arafat, the Palestinian Authority leader, to give Mahmoud Abbas, the Palestinian Prime Minister, adequate security forces to restrain “terrorist” groups. America has previously sided with Israel in ignoring Mr Arafat. The intense pressure already bearing down on the peace process exploded into a full-blown crisis within a few seconds yesterday, when five air-launched missiles slammed into Ismail Abu Shenab’s car as it travelled through the heart of Gaza City.

The car was hit near Gaza’s Islamic University, where Mr Abu Shenab worked as an engineering lecturer. His two bodyguards were also killed and 15 bystanders were injured.

Witnesses said that Mr Abu Shenab and his bodyguards had tried to get out of the blazing car after the first missile struck, but died after three more missiles landed in quick succession. They said that a fifth exploded as people in nearby shops and houses approached the car to help. Hours after the strike, the charred remains of the car lay on its roof as children scavenged for spare parts.

The deaths came after Israel’s security Cabinet approved a return to the controversial policy of so-called “targeted killings” of leading militants as part of measures to quell Palestinian violence.

It provoked bitter denunciation, however, from Palestinians, who insisted that Mr Abu Shenab, 53, was Hamas’s leading advocate of negotiations with Israel. They said that he had vigorously supported a ceasefire declared to help Mr Abbas implement the road map. Mr Abu Shenab’s son, Hamza, 19, also said that his father had believed in the ceasefire and had said that he was ready to accept a two-state solution, as advocated by the road map.

Mr Abbas called Israel’s action “an ugly crime” and suggested that it would result in him scrapping his own plan to contain Hamas, announced after Tuesday’s suicide bombing. He added: “This is against peace and the peace process. It will for sure affect the whole process and the decision taken by the Palestinian Authority.” Hamas leaders announced that they were ending the ceasefire and swore revenge against Israel. Palestinians launched three home-made rockets in Gaza last night, but no injuries were reported.

At a wake just yards from Mr Abu Shenab’s home, Abdel Aziz al-Rantissi, a fellow Hamas leader who narrowly escaped death in an Israeli missile strike in June, accused Ariel Sharon, the Israeli Prime Minister, of deliberately torpedoing the road map. “Sharon really was against the hudna (ceasefire) and so he has assassinated it. The hudna is dead,” Mr Rantissi said. “Retaliation will be decided on by our military wing.”

Insisting that Hamas had been ready to continue the ceasefire until yesterday’s strike, he denied that the organisation’s leadership in Gaza had sanctioned the Jerusalem suicide bombing, carried out by Hamas militants from Hebron in the West Bank.

“This was a decision by the military leadership in Hebron,” he said. “There is no connection between us and the West Bank except by mobile phone, and it is impossible to use mobile phones for military actions. So each area prepares its own operations independently.”

Israeli officials were unrepentant over Mr Abu Shenab’s killing. “He was a murderer,” Ehud Olmert, Israel’s Industry and Trade Minister and a close ally of Mr Sharon, said. “I hope it is a lesson for the Hamas people. But it is not enough, we have to get to each and every Hamas leader.”

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