Tony Blair today cancelled a planned visit to Gaza in his role as Middle East peace envoy after what his spokeswoman described as threats made against him.

The planned trip would have been the highest-level diplomatic mission to the territory since the militant Hamas group seized control of it a year ago.

Ruti Winterstein, Blair's spokeswoman, said the visit had been called off because of "specific threats" against the former prime minister, giving no further details.

The decision was taken very much at the last minute – members of the former prime minister's entourage arrived at Israel's Erez Crossing into Gaza this morning and waited for two hours before the cancellation was announced, Reuters reported. Blair was not with them.

Another spokesman for Blair, Matthew Doyle, said the decision was taken "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," Doyle added.

An Israeli diplomatic source told Reuters that Blair called off the visit after Israel's defence minister, Ehud Barak, told him of "a threat that could materialise as he entered the Gaza Strip".

Blair had been expected to meet traders and inspect a sewage project being built with international funds. He had not been due to meet any officials from Hamas, viewed by Israel, the US and EU as a terrorist organisation.

UN officials in Gaza told Reuters Blair still hoped to visit the territory in the future, although no new date had been set.

Before the visit Hamas said it was making "all the necessary security arrangements". Although the group has largely pacified the strip, several other small militant groups are believed to still operate there.

A spokesman for Hamas, Taher Nunu, said Blair would not have been at risk on the visit and added: "Gaza is still open for all visitors, to break the siege and see the extent of suffering here".

Hamas, which won Palestinian-wide elections in 2006, hoped Blair's presence would mark an end to its complete ostracism by western nations. In June last year Hamas pushed the more moderate Fatah movement of the Palestinian president, Mahmoud Abbas, out of Gaza.

The trip was due to come nearly a month after an Egyptian-brokered truce largely ended cross-border fighting between Israel and Palestinian militants.

The quartet of powers involved in Middle East peace efforts - the US, EU, Russia and the UN - appointed Blair as envoy a year ago with a particular focus on economic reconstruction.

Thus far most of the projects promoted by Blair have been designed for the West Bank, where Fatah are still in control.