"I firmly believe that the sanctions policy that we are pursuing will work, but I am not one who is going forward to say that we rule out any particular form of action," Brown said at his first press conference as premier.

"But I firmly believe that the sanctions that we are imposing on Iran are sanctions that are having an effect already," he told reporters at 10 Downing Street in London.

"We are going to have to consider what we do in future, there will probably be a third (UN Security Council) resolution in relation to Iran soon and I believe that that is a way forward that is working and will work," he said.

"And again I appeal to the Iranian authorities to understand the fears that other countries have about the development of a nuclear weapons programme," he said.

The UN Security Council has imposed two rounds of sanctions to get Tehran to cease enriching uranium and stop building a heavy-water reactor in Arak, along with cooperating fully with the inspectors from the International Atomic Energy Agency (IAEA).

Iran has since April blocked inspectors visiting the heavy-water reactor. Such reactors produce plutonium, which can be used to make nuclear weapons. The other main atom bomb material is enriched uranium.

Iran has rejected any halt in its enrichment work, claiming a right to it under the Non-Proliferation Treaty.

On July 13, the United States said it was skeptical of Tehran's agreement to allow IAEA inspections of the reactor.

Iran insists its nuclear programme is a peaceful effort to generate electricity, but the United States and Britain fear it is a cover for developing atomic weapons.

Iran and the IAEA are to hold a fresh round of talks in Vienna this week.

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