Shimon Peres, the Israeli Prime Minister, said yesterday that Israel may delay its withdrawal from Hebron, the capital of the southern West Bank, unless Yasser Arafat, the Palestinian leader, clamps down on Islamic militants.
In the wake of last Sunday's suicide bombs, which killed 25 Israelis, opinion polls show Mr Peres for the first time being beaten in an election by Binyamin Netanyahu, the leader of the right-wing Likud party by 51 per cent to 45 per cent.
At a late-night meeting Mr Arafat was told by Lieutenant-General Amnon Lipkin-Shahak, the Israeli chief of staff, that Israel wanted 15 members of Hamas, the Islamic organisation, arrested and sentenced to long prison terms.
He also demanded that Mr Arafat move against Hamas as a political movement and not just against its military wing, known as the Izzedine al-Qassim brigades.
There is growing evidence, however, that Hamas is split and the latest bombings were carried out by a cell which does not obey orders from the political leadership. Izzedine al-Qassim in Gaza said "there is no connection" between its organisation and the two attacks.
In Hebron, Khalid Amayreh, an Islamic commentator, said yesterday: "I believe it was a splinter group within the Islamic movement which was responsible."
It is possible that Hamas is distancing itself from the attacks to avoid retaliation by Mr Arafat and Israel. For security reasons, Mr Amayreh says, the Izzedine al-Qassim cells on the West Bank operate with little control from the centre.
He believes that Hamas wanted to regain face after the assassination of Yahyah Ayyash, its master bomb-maker, in January but "the most important thing for the organisation is a modus vivendi with the Palestinian Authority."
As Mr Peres sees his chances of victory in the election on 29 May increasingly in doubt, he is making almost desperate efforts to reassure Israelis that he is doing everything he can for their security. He announced yesterday that Palestinians would continue to be forbidden entry to Israel from the West Bank and Gaza and a special headquarters in charge of security on buses will be set up. He said he would demand Mr Arafat disarm Hamas, Islamic Jihad and other groups. If the Palestinian leader did not act, Mr Peres said, the withdrawal from Hebron next month would be in doubt.
The bombs have already saved Mr Netanyahu and Likud from what appeared an inevitable defeat. They have ended the political honeymoon Labour has enjoyed since the assassination of Yitzhak Rabin, the prime minister, in November. Mr Netanyahu's hopes of victory are also being boosted by talks with David Levy, the influential former foreign minister, who had broken with Likud to form his own party, called Gesher. Mr Levy is prepared to take his party into Likud if he is guaranteed seven seats in the 120- member Knesset, twice as many as he could expect to win if he stands on his own.
This may be too great a price for members of Likud. Mr Netanyahu, whom political observers were beginning to write off a week ago, is trying to ensure that he does not slip back in the polls as the emotional reaction to Sunday's bombings becomes less intense.
At a press conference yesterday he said he would continue peace negotiations with the Palestinians, but would refuse to meet Mr Arafat.
He said that he would "send the tanks into the autonomous areas" but believed he knew of ways to stop suicide bombers.