Israeli peace groups and Palestinian officials say thousands of homes are under construction in the main settlements, in addition to an expansion of Jewish outposts that are illegal under Israeli law. Mr Sharon has promised the US he will dismantle the outposts, which are usually clusters of containers or trailer homes serviced by government-built roads, but has failed to do so.

One Israeli group, Settlement Watch, says in the three months to May, West Bank settlements expanded by 26 hectares (65 acres).The government has approved construction of thousands more homes in the three main settlement blocs on the West Bank, encouraged by an apparent endorsement by George Bush for their eventual annexation.

In a letter to Mr Sharon, Mr Bush praised the Gaza pullout and agreed that "in light of new realities on the ground, including already existing major Israeli populations centres", it was unrealistic to expect a full return to the 1967 borders.

Dror Etkes, head of Settlement Watch, said that the expansion of Jewish outposts and continuing house building since Mr Sharon announced his plan in December was evidence that the government was seeking more territory.

"The government is trying to push the boundaries of the settlements as much as possible before they are frozen," he said. "The new rule of the game we have seen in past weeks is the diameter of permitted construction area in the West Bank has grown. The purpose is to expand as fast as possible because of negotiations with the US to limit future construction to areas already under construction."

American officials have been appointed to agree limits to settlement expansion in order, Washington says, to preserve land for a future Palestinian state. Mr Sharon is pressing the US to allow building to continue in areas already under construction, to cater for the "natural growth" in families.

But Settlement Watch says aerial photographs reveal that in some settlements, construction has begun on the outer limits of the municipal boundaries, often some distance from the settlement. It believes the government will claim the right to build on the intervening territory or use the outposts to link settlements.

The pictures show new houses, roads and other infrastructure around about 12 of the 90 or more outposts, sometimes linking them to established colonies.

Last week Ephraim Sneh, an opposition Labour party MP, presented photographs of the outposts and infrastructure expansion to his party's caucus in parliament.

"In blunt violation of the promise to the US president, the government doesn't dismantle the illegal outposts. With government money they are expanded, asphalt roads are paved - all the necessary preparations to turn them into permanent settlements," he told the Guardian.

"It casts a shadow on the real intent of Sharon's disengagement plan. The disengagement may be just a cover for the real intention of the prime minister to deepen and solidify the Israeli hold in the West Bank." He added that the expansion was possible only with official cooperation. "It can't be done without government encouragement and financing," he said. In May, the state comptroller said Israel's housing ministry had illegally funnelled about £3.8m to fund unauthorised settlement expansion, half of it to the illegal outposts.

Incentives

Last month, the defence and finance ministries authorised a £37m budget to fortify settlements outside the steel and concrete barrier Israel is building through the West Bank. Last week, it was revealed that dozens of prefabricated homes which the government had authorised for established settlements were sent to the outposts.

"This is a well-placed deal cut between the settlers in the area and the ministry of defence," said Mr Etkes. "If they're dismantling at times there is the immediate intensification of construction of another outpost in the area."

The government is offering additional incentives to persuade Israelis to move to empty housing on the settlements and newly arrived Jews frequently find themselves placed there. But concrete and asphalt are more important than people in staking Israel's claim to the West Bank.

Last month, Shaul Mofaz, the defence minister, told the civil administration in the West Bank - which is under military control - to draw up plans for rapid expansion of the Etzion settlement block near Bethlehem. In recent weeks, the government has approved expansion of Efrat, part of Etzion bloc, which is also expanding into what was the Palestinian village of Walaja.

"The land was taken by the Jewish National Fund," said Jeff Halper, a veteran Israeli campaigner against settlement expansion. "Almost every house has a demolition order."

Mr Mofaz also reassured settlers' leaders of continued expansion of the other two main blocs in the West Bank, Ariel and Ma'ale Adumim, which already eat into Palestinian territory.

Mr Halper said that the government planned to more than double the size of Ma'ale Adumim, east of Jerusalem, to provide homes for about 70,000 people

Ehud Olmert, Israel's deputy prime minister, who rarely makes policy statements without Mr Sharon's approval, recently said that Jewish West Jerusalem must grow to Ma'ale Adumim.

The Israelis are also looking further east to Mitzpe Jericho, which is home to about 1,500 people. Giant billboards picturing clusters of blocks of flats mark the limits of the municipality several miles from the existing housing.

"The government plans to link Jerusalem to Ma'ale Adumim and Ma'ale Adumim to Mitzpe Jericho. Eventually it will all fall under the Jerusalem municipality. Jerusalem is being transformed from a city into a region," said Mr Halper.

Mr Sharon's spokesman, Raanan Gissin, denied West Bank settlements were being expanded, saying that construction remains within the existing boundaries.

"Anything that is illegal will be removed as the prime minister has promised the Americans," he said of the outposts.