Tony Blair hastily cancelled his visit to the Gaza Strip today and headed back to Jerusalem after receiving what his aides described as a "specific security threat" minutes before crossing the border.

With his advanced security party having already gone through the Erez passenger crossing into the territory at 9.45am local time, the international peace envoy's motorcade was ordered to turn around and abort its journey.

The Israel Security Agency said it had received “pinpoint information that Palestinians were planning to attack Blair in Gaza, so the relevant services alerted him to the fact.”

Details of the threat against Mr Blair, who aimed to visit infrastructure projects in his capacity as international Middle Eastern peace envoy, are unknown.

However, as well as security fears, it may have been postponed for diplomatic reasons, as Mr Blair would have had to pass through several Hamas military checkpoints to get to the sites he was visiting, a prospect which it is believed may have caused diplomatic embarrassment, as the West currently has no relations with the territory's Islamist rulers.

The former Prime Minister had not scheduled any meetings with Hamas officials, but the organisation had made security arrangements for the visit, setting up checkpoints in areas he was expected to tour, banning cars from using roads, and lining streets with black-clad policemen carrying AK-47s.

Mr Blair would have been the first major international official to visit the Gaza Strip since Hamas seized power last summer.

Matthew Doyle, Mr Blair’s spokesman, said the envoy called off the visit “due to a specific security threat which would have made it irresponsible to proceed, not just for those visiting but also the local community.

“He looks forward to being able to go to Gaza again in the future and will of course in the meantime continue to work to improve the conditions for the people there.”

Mr Blair had been expected to visit schools and a sewage treatment plant in the town of Beit Lahiya, which make up part of internationally sponsored regeneration and investment initiatives designed to improve Palestinian infrastructure.

He also cancelled a visit expected to Sderot, a town in southern Israel which is the frequent target of rockets fired by Palestinian militants in Gaza.

Taher Nunu, a Hamas spokesman, denied there were any security threats against Mr Blair. “Gaza is still open for all visitors, to break the siege and see the extent of suffering here,” he said.

Mr Blair last visited Gaza in 1998 when he was Prime Minister. The Quartet — the United States, the European Union, Russia and the United Nations — appointed him to the post of envoy a year ago with a focus on economic improvement, to bolster the chances of a peace deal this year.

Since the takeover by Hamas, Gaza has been virtually sealed off from the world by Israel and Egypt, a policy that has received tacit international backing.

Mr Blair has said in recent weeks that a new policy towards Gaza needs to be developed, pointing to the growing suffering of Gaza’s people, but has not offered a plan. The options are limited because much of the international community considers Hamas a terrorist group and has shunned its government.

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