U.S. President Bush and British Prime Minister Gordon Brown say they are working to extend sanctions against Iran's nuclear program. VOA White House Correspondent Scott Stearns reports, the two leaders met to discuss wars in Iraq and Afghanistan as well as political unrest in Zimbabwe.

President Bush says Iran's leaders can not be trusted to maintain a uranium enrichment program that they say is intended only for generating electricity.

"They have proven themselves to be untrustworthy. To say that it's OK to let them learn to enrich and assume that that program that knowledge couldn't be transferred to a military program is in my judgment naïve," he said.

The president and prime minister spoke to reporters in the White House Rose Garden after private talks in the Oval Office.

The head of the U.N. nuclear agency says Iran continues to build centrifuges to enrich uranium in defiance of sanctions. But Mohamed El Baradei says the country's progress has been slow.

Iranian President Mahmoud Ahmadinejad last week announced plans to install 6,000 new centrifuges to enrich uranium. Highly-enriched uranium can be used to generate electricity or to fuel a nuclear weapon.

Prime Minister Brown says he makes no apologies for pushing to extend the three sets of sanctions the U.N. Security Council has already imposed against Iran.

"We will extend sanctions where possible on Iran. Iran is in breach of the nonproliferation treaty. Iran has not told the truth to the international community about what its plans are. And that's why I am talking to other European leaders about how we can extend European sanctions against Iran," he said.

The two leaders vowed to continue fighting Taleban militia in Afghanistan and say they are encouraged by progress on more troops for that effort following this month's NATO summit.

President Bush thanked Prime Minister Brown for the sacrifices of British troops in Iraq, particularly during the recent fighting in the southern city of Basra.

The prime minister says Iraq is now a democracy that is moving forward both economically and politically as coalition troops train Iraqi forces to handle more of their own security.

Both leaders called on Zimbabwe's electoral commission to release the results of last month's presidential election. Opposition leaders say they defeated long-time ruler Robert Mugabe. The ruling party wants a recount.

President Bush thanked Prime Minister Brown for speaking-out about Zimbabwe at the United Nations.

"You can't have elections unless you are willing to put the results out," he said. "What kind of election is it if you don't let the will of the people be known?"

Mr. Bush says more African leaders need to speak out on Zimbabwe, and the United Nations and the African Union must play an active role in resolving the electoral dispute.

Before his White House meeting, Prime Minister Brown met separately with the three U.S. Senators hoping to replace President Bush: Republican John McCain and Democrats Hillary Clinton and Barak Obama.

Mr. Brown says it is up to Americans to decide their next leader, but he has no doubt relations between the United States and United Kingdom will remain close whatever the outcome.

"What I was convinced of after talking to each of them and talking about the issues that concern them and concern the world is that the relationship between America and Britain will remain strong, will remain steadfast, and will be one that will be able to rise to the challenges of the future," he said.

The prime minister says he looks forward to continuing a discussion with all three candidates over the next few months. Americans choose their next president in November.