In the first speech to the Israeli Knesset by a British prime minister, Gordon Brown is to warn Iran today it faces growing isolation if it rejects an offer from major powers on its disputed nuclear programme.
Brown will pledge to stand by Israel and condemn threats against the country by Iranian President Mahmoud Ahmadinejad, according to excerpts of the speech released by his office in advance.
"Iran now has a clear choice to make: suspend its nuclear programme and accept our offer of negotiations or face growing isolation and the collective response not of one nation but of many nations," Brown is to say.
"Just as we have led the work on three mandatory sanctions resolutions of the United Nations, the UK will continue to lead -- with the U.S. and our European Union partners -- in our determination to prevent an Iranian nuclear weapons programme."
The United States, Britain, France, Germany, Russia and China have offered Iran financial and diplomatic incentives to halt nuclear activity which the West fears is a cover for making bombs. Tehran says it is aimed solely at generating electricity.
After talks in Geneva ended in stalemate on Saturday, six major powers gave Iran two weeks to answer calls to rein in its nuclear activities or face tougher sanctions.
British government officials travelling with Brown said if Iran did not accept the incentives, the next step would be to ratchet up sanctions against Tehran, possibly including sanctions on Iran's oil and gas industry.
They said such sanctions could seek to target Iran's domestic energy market by making it difficult for Iran to obtain equipment and spare parts for its refineries.