Mr Netanyahu joined Mr Sharon's government as foreign minister on Wednesday with a promise to work with him amicably in the run up to January's general election, although both will seek the nomination to stand as prime minister.

But within hours he was staking out a position to the right of Mr Sharon by renouncing the possibility of an independent Palestinian state, backing the expansion of Jewish settlements in the occupied territories, and threatening to banish Yasser Arafat from the West Bank.

The White House has Mr Sharon's promise that Israel agrees in principle to an independent Palestinian state, will freeze new Jewish settlements, and will not exile or harm Mr Arafat.

Mr Netanyahu's contrary position had the US government seeking assurances that the Israelis will not stray from the agreed policies and increase the tension in the Middle East as it prepares a military campaign against Iraq.

But, so far at least, Mr Netanyahu's belligerence has not done him much good with the voters.

Opinion polls show him trailing Mr Sharon by 10 points in the race for the Likud party leadership.

But whichever of them is chosen will have a healthy lead over the Labour opposition, which holds its primaries in 10 days, the polls show.

They put the leftwing mayor of Haifa, Amram Mitzna, who promises immediate negotiations with Mr Arafat, ahead in the Labour contest.

Mr Netanyahu fares best on only one issue: the economy, on which he has more than twice as much support as the prime minister.

But the forthcoming prime-ministerial and parliamentary elections, like so many others in Israel, are about security, and Mr Sharon commands the confidence of six out of 10 voters on that issue.

Mr Netanyahu tried to gain support on the security issue by implicitly blaming Mr Sharon for "the tremendous escalation of terror" and promising a harder line against the Palestinians.

He also raised doubts about the American road map to a peace settlement, which envisages a Palestinian state within three years.

Mr Sharon has agreed to that in principle, even though he shows little inclination to make it happen any faster than he has to.

In an interview published in yesterday's Jerusalem Post, Mr Netanyahu ruled out the possibility of a Palestinian state, speaking rather of self-rule, on the grounds that full Palestinian independence would threaten Israel's security.

"We can and must resist the Palestinians' efforts to achieve the powers that would endanger the state of Israel, like the fielding of an army... The ability to have certain sovereign powers that have nothing to do with self-determination must be withheld," he said.

"The Palestinians have a right to self-rule. But allowing them the powers that could destroy the one and only Jewish state is not a prescription for peace. It is a prescription for catastrophe."

Mr Sharon has hit back, without naming Mr Netanyahu, by implying that his foreign minister is putting relations with Israel's closest ally, the US, in danger.

"I will not tolerate harm to our international relations, harm that might seriously damage our international standing and our efforts to [obtain] economic assistance," he said.

The disagreements between the two men are not limited to policy differences.

They are also fighting over the timing of the general election, which must be held by early February, and of the Likud primaries.

Mr Sharon favours an early vote in both instances, presumably because he believes it will curtail Mr Netanyahu's ability to organise.