WASHINGTON (CNN) -- President Bush and British Prime Minister Gordon Brown discussed a range of topics at the White House on Thursday including terrorism, fighting in Iraq and Afghanistan, Iran and economic issues, Bush told reporters afterward.

"I'm pleased to welcome a good friend to the Oval Office, and we had a good discussion. I appreciate our good relationship with Great Britain," Bush said at the start of a joint news conference in the White House Rose Garden.

Britain understands the threats from terrorism, Bush said.

"He shares our determination that these evil men must be stopped." Watch more of the news conference »

The president said he appreciates the contributions of British troops in Iraq and Afghanistan. Britain has nearly 8,000 forces around Basra, in southern Iraq.

"We're making progress," Bush said. "Failure in Iraq will send a message to Iran that the United States and its allies were not intent on making sure they stay within the borders of their country. ... It's worth it to succeed."

Brown added, "The world owes George Bush a huge debt of gratitude" for his efforts against terrorists.

The prime minister condemned Iran for failing to verify it has stopped enriching uranium for possible use in nuclear weapons, and he said he supports expanding sanctions against that country.

Bush said it is "naive" to think Iran can't transfer nuclear enrichment knowledge from energy uses to producing an atomic bomb.

Brown expressed concern about food shortages in developing nations, and pledged to work with the World Food Programme to address ways to increase food production.

"We must act immediately and we must have a long-term plan," he said.

Both men pressed Zimbabwe to release the results of its recent presidential election.

"You can't have elections and not put the results out," Bush said.

It is Brown's second U.S. visit since taking office in November.

Before his meeting with Bush, Brown met with the three U.S. presidential candidates -- Democratic Sens. Hillary Clinton and Barack Obama, and Republican Sen. John McCain -- at the British residence in Washington. E-mail to a friend

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