President Bush and British Prime Minister Gordon Brown jointly pledged to step up efforts to thwart Iran’s nuclear enrichment program and work with European leaders to increase sanctions on the country during a press conference outside the White House on Thursday.

Bush called it “naïve” to believe that Iran is not intending to transfer its nuclear enrichment capabilities from energy development to atomic bomb production. Bush described Iran as “untrustworthy,” and said that if the country “learns how to enrich, it is knowledge which can be used to develop a nuclear weapon.”

“Gordon Brown seriously sees the threat, as do I, and now it’s time to confront the threat,” he said.

Brown, who is on his second visit to the United States since succeeding Tony Blair as prime minister in June, echoed Bush’s sentiments on Iran and praised him for his commitment to fighting global terrorism.

"The world owes President George Bush a huge debt of gratitude for leading the world” in the fight against terrorism, Brown said. "No international partership has served the world better than our special relationship ... the bond between our two countries is stronger than ever."

"We will continue to work together with the strengthening efforts we are making ... with Iraq and Afghanistan," he said.

The two leaders also upheld their commitment to a military presence in Iraq and agreed that both political and financial progress was being made in the country.

Bush said that failure in Iraq would embolden Al Qaeda and Iran, and send a message to U.S. allies that "you can't count on America."

Brown, who praised both U.S. and British troops serving in Iraq and Afghanistan, said that "progress is Iraqis now being able to take control of their own affairs," and that the eventual goal is to move from "combat to overwatch."