Britain is due to break new diplomatic ground next week with talks in Iran by Jack Straw, foreign secretary, in a wide-ranging effort to bolster support for the US-led campaign against terrorism.

Mr Straw will be the first UK foreign secretary to visit Iran since the Islamic revolution that toppled the Shah 22 years ago.

British officials said he would try to build on Iran's "positive" response to the crisis. Mr Straw hopes to meet Mohammad Khatami, the reformist Iranian president.

Although the talks were officially described as bilateral, they extend the active role that Tony Blair, prime minister, has developed as an advocate of the US following last week's terrorist attacks.

The hastily arranged talks are being added to a lightning Middle East tour that Mr Straw is set to begin on Tuesday. This will include meetings with Israeli, Palestinian and Jordanian leaders.

They form part of an intensive series of contacts that the US and allies have held with Afghanistan's neighbours to enlist co-operation with a US-led response or other forms of support.

Iran, which has had tense relations with Afghanistan's Taliban regime, has said it will not permit its air space to be used in any retaliation, although it expressed solidarity in condemning last week's atrocities in the US. It has declared its interest in a UN-led retaliatory move and a wider global fight against terrorism, but is unlikely to prove forth- coming in backing a US operation against Afghanistan.

"It's important to build alliances with every country that we can," Mr Straw said on Friday.

The Tehran talks were fixed in a telephone conversation between Mr Blair - who arrived in Brussels on Friday from the US - and Mr Khatami.

The UK has had a number of ministerial contacts with Iran since the two countries re-established relations in 1998.

Mr Straw, who had intended to go to Iran later this year, talked by phone earlier this week with his Iranian counterpart, Kamel Kharrazi. Officials said he would discuss a number of terrorism-related issues, including terrorist financing and controls on arms exports.

Mr Straw on Friday cited Tehran's "powerful" opposition to the Taliban's fundamentalist regime in Afghanistan and referred to Iranian fears of a further increase in the country's 2m-plus Afghan refugees.

"Iran has suffered very badly as a result of the instability and extremism of the Taliban, and has had to face a very, very serious refugee problem on its border," he said.