The Israeli Prime Minister, Ehud Olmert, has been discussing plans to set permanent borders for Israel with his British counterpart, Tony Blair.
It is his first meeting with the British prime minister since his election win in March.
The UK, like other countries, wants Israel to negotiate with the Palestinians on border changes.
Mr Olmert pledged to make every effort to seek a deal with the Palestinians before drawing borders unilaterally.
At a news conference, the two men agreed that negotiations could only be held if there was a renunciation of violence and an adherence to the peace "road map".
Asked if he advocated talks with the militant Hamas leadership, Mr Blair said: "You can only negotiate with people who accept your existence and stop violence. A negotiated settlement is easily, manifestly the best thing."
"We can't continue indefinitely with what we have at the moment. We need a resolution or it slips back into chaos," he said.
He said there was agreement within the international community for a negotiated settlement on a two-state system.
And he promised Mr Olmert "every support and every impetus" towards that goal.
Iran nuclear plans
Mr Olmert said he had reassured the British prime minister that he would "make every possible effort to engage in dialogue with the Palestinians".
But he told reporters he had outlined what would happen if negotiations with the Palestinians fail, which includes pulling out of parts of the West Bank and "realigning" Israeli settlements.
The two men said they also discussed Iran's controversial nuclear programme.
"Israel will not tolerate nuclear weapons in the hands of Iran. We will not be able to accept such a reality," Mr Olmert told reporters. "It is quite obvious why."
Mr Olmert was elected on a programme to settle Israel's permanent borders by 2010, whether through negotiations with the Palestinians or not.
He is offering a partial withdrawal from the West Bank.
The Palestinians, however, have accused Israel of seeking a unilateral solution to its advantage as land captured and occupied in the 1967 war would still be occupied.
The Islamic militant group Hamas, which took charge of the Palestinian government after elections in January, refuses to recognise Israel.
Israel and Hamas have also been squaring off against each other in the wake of the deaths of eight Palestinian civilians last Friday, apparently by Israeli shelling.