British Prime Minister Gordon Brown said on Monday that London would seek a worldwide ban on oil and gas investment in Iran if Tehran continued to defy the international community over its nuclear program in what he called a policy of "hard-headed internationalism."
Brown, in a major foreign policy speech in London on Monday evening, also described himself as a "lifelong admirer of America" who would have "no truck" with anti-Americanism in Britain or elsewhere in Europe.
The British leader was giving his first address to the annual Lord Mayor's banquet in the City of London since he took over as prime minister at the end of June.
The occasion, which brings together influential forces from politics and business, is traditionally used by British leaders to spell out foreign policy goals.
Commentators said Brown was keen to stress that he was as much a believer in the "special relationship" between Britain and the US as Tony Blair, his predecessor, while also making clear that contemporary issues and conflicts required a global response.
Brown said Britain would urge both the EU and the UN to impose tougher sanctions on financial sector dealings with Iran.
"Iran should be in no doubt about the seriousness of our purpose," he said, adding that action should follow unless there were "positive outcomes" from two major reports on Iran's activities due in the near future.
"We will lead in seeking tougher sanctions both at the UN and in the European Union, including on oil and gas investment and the financial sector," Brown said.
Iran had a choice between confrontation and the transformation of its relations with the international community, he said.
"My approach is hard-headed internationalism -- internationalist because global challenges need global solutions and nations must cooperate across borders, often with hard-headed intervention -- to give expression to our shared interests and shared values," the prime minister said.
"And hard-headed because we will not shirk from the difficult long-term decisions and because only through reform of our international rules and institutions will we achieve concrete, on-the-ground results," Brown said.
Stressing the importance of Britain's relations with the US, he said: "It is no secret that I am a lifelong admirer of America. I have no truck with anti-Americanism in Britain or elsewhere in Europe and I believe that our ties with America -- founded on values we share -- constitute our most important bilateral relationship."
He added that it was "good" for Britain, for Europe and for the wider world that France, Germany and the EU were also building stronger relationships with the US.