President George Bush and prime minister Gordon Brown announced new sanctions on Iran during a joint press conference today.
The conference followed what are expected to be president Bush's final talks with Mr Brown after he spent the morning with old ally Tony Blair.
Options against Iran include seizing the overseas assets of its biggest bank and new sanctions on oil and gas.
It's the second day of Mr Bush's visit to Britain, although he used the occasion to cast doubt on whether it really will be his last.
"This has been a good trip," he said. Some are speculating this is my last trip. Let them speculate, who knows?"
That news will not be welcomed by the hundred of anti-war protestors who made themselves heard in Westminster yesterday while Mr Bush had dinner with the Queen.
However, the estimated 2,000-strong demonstration was muted when compared to the 200,000 people who turned out to protest the president's last UK visit in 2003.
Police said 25 activists were arrested after scuffles broke out yesterday.
Mr Bush is approaching the end of his European farewell tour, having already visited Italy, France and Germany.
Mr Bush has now arrived in Northern Ireland for the next stage in his trip.
Flanked by first minister Peter Robinson and deputy first minister Martin McGuinness at Stormont Castle, Mr Bush said: "Societies around the world wonder if reconciliation is possible for them. The progress made today was unimaginable years ago."
Mr Robinson said: "We're delighted president Bush of his own choice has realised Belfast is one of the majoy cities of Europe. We're really grateful for the work that has been done by the president over recent years."
Eight years of Bush administrations will end this year, with either presumptive Republican and Democratic nominees John McCain or Barack Obama poised to replace the president.