At the northern edge of Jerusalem, on the main road to the Palestinian city of Ramallah, three towering concrete walls are converging around a rapidly built maze of cages, turnstiles and bomb-proof rooms.
When construction at Qalandiya is completed in the coming weeks, the remaining gaps in the 8m (26ft)-high walls will close and those still permitted to travel between the two cities will be channelled through a warren of identity and security checks reminiscent of an international frontier.

The Israeli military built the crossing without fanfare over recent months, along with other similar posts along the length of the vast new "security barrier" that is enveloping Jerusalem, while the world's attention was focussed on the Israeli prime minister, Ariel Sharon's removal of Jewish settlers from the Gaza Strip.

But these de facto border posts are just one element in a web of construction evidently intended to redraw Israel's borders deep inside the Palestinian territories and secure all of Jerusalem as Israel's capital, and to do it fast so as to put the whole issue beyond negotiation. As foreign leaders, including Tony Blair, praised Mr Sharon for his "courage" in pulling out of Gaza last month, Israel was accelerating construction of the West Bank barrier, expropriating more land in the West Bank than it was surrendering in Gaza, and building thousands of new homes in Jewish settlements.

"It's a trade off: the Gaza Strip for the settlement blocks; the Gaza Strip for Palestinian land; the Gaza Strip for unilaterally imposing borders," said Dror Etkes, director of the Israeli organisation Settlement Watch. "They don't know how long they've got. That's why they're building like maniacs."

At the core of the strategy is the 420-mile West Bank barrier which many Israeli politicians regard as marking out a future border. Its route carves out large areas for expansion of the main Jewish settlements of Ariel, Maale Adumim and Gush Etzion, and expropriates swaths of Palestinian land by separating it from its owners.

In parallel, new building on Jewish settlements during the first quarter of this year rose by 83% on the same period in 2004. About 4,000 homes are under construction in Israel's West Bank colonies, with thousands more homes approved in the Ariel and Maale Adumim blocks that penetrate deep into the occupied territories. The total number of settlers has risen again this year with an estimated 14,000 moving to the West Bank, compared with 8,500 forced to leave Gaza.

Israel is also continuing to expand the amount of territory it intends to retain. In July alone, it seized more land in the West Bank than it surrendered in Gaza: it withdrew from about 19 square miles of territory while sealing off 23 sq miles of the West Bank around Maale Adumim.

Israel's strategy is to "strengthen the control over areas which will constitute an inseparable part of the state of Israel", the prime minister said after the Gaza pullout.

Last month, he told a meeting of his Likud party allies that it was important to expand the settlements without drawing the world's attention. "There's no need to talk. We need to build, and we're building without talking," he said. A few days later, one of the prime minister's senior advisors, Eyal Arad, publicly advocated "a strategy of unilaterally determining the permanent borders of the state of Israel".

The greatest impact of recent Israeli actions has been in and around Jerusalem, as Israel stepped up construction of the wall along the most controversial part of its route.

"What we are seeing is an acceleration of construction of the barrier," said David Shearer, head of the UN's Office for the Coordination of Humanitarian Affairs in Jerusalem.

"Because of the barrier, Jerusalem is being sealed off from the rest of the West Bank. Movement in Jerusalem will be with a magnetic card and a sophisticated system of gates. The access the Palestinians have enjoyed to their places of worship, to some of the best schools, to hospitals is now going to be severely restricted."

The concrete wall through Jerusalem carves out Arab enclaves in the city, restricts the growth of non-Jewish neighbourhoods and separates some 200,000 Palestinian residents from the occupied territories.

East Jerusalem will be further isolated from the rest of the West Bank by moves to link the city with Maale Adumim settlement using the barrier to mark out a boundary. The effect will be to entirely surround the Arab areas of Jerusalem with large Jewish neighbourhoods and to push Israel's frontier almost half way across the West Bank, virtually severing the north and south of the Palestinian territory at its narrowest point.

Organisations such as the International Crisis Group say it could have potentially explosive consequences. "Current policies in and around the city will vastly complicate, and perhaps doom, future attempts to resolve the conflict by both preventing the establishment of a viable Palestinian capital in Arab East Jerusalem and obstructing the territorial contiguity of a Palestinian state," it said in a recent report.

"The measures currently being implemented are at war with any viable two-state solution and will not bolster Israel's safety; in fact, they will undermine it, weakening Palestinian pragmatists, incorporating hundreds of thousands of Palestinians on the Israeli side of the fence, and sowing the seeds of growing radicalisation."

In recent years, both sides have generally accepted that a negotiated agreement would leave the main settlement blocks close to Jerusalem in Israeli hands. Last year, Mr Bush wrote to Mr Sharon assuring him that Israel would not be expected to return to the 1967 borders "in light of new realities on the ground, including already existing major Israeli population centres".

But Daniel Seidemann, an Israeli lawyer fighting legal cases over the barrier, said the government has worked to make those realities on the ground as extensive as possible while foreign governments shied away from criticism of Mr Sharon for fear of jeopardising the Gaza pullout.

"It's clear what's happening. It's clear the wall is used to designate the border that Sharon thinks he can get with the Americans," he said.

Mr Sharon appears to be counting on continued silence from America and European capitals because he faces a general election next year that Washington would like to see him win over his main challenger on the far right, Binyamin Netanyahu.

The Palestinian leadership believes Mr Sharon has little incentive to negotiate because the Palestinians will not agree to surrender their claim to East Jerusalem or the large areas of land he wants to annex.

But Yossi Beilin, a former Israeli cabinet minister and a peace negotiator, said that a lack of pressure from Washington and other members of the Quartet overseeing the "roadmap" peace plan leaves Mr Sharon free to redraw Israel's borders.

"The commitment to the roadmap is a big joke. It's hot air all the time," Mr Beilin said.

"I'm very pessimistic. I see the big gap between the speeches - how high the roadmap is on the agenda and how foreign governments say they have to deal with it - and nothing is happening on the ground. Nothing. Sharon just does what he wants."