During Mr Bush's visit to Russia, the two men had what he called a "frank" discussion over Moscow's support for Iran's nuclear power programme.

We spoke very frankly and honestly about the need to make sure that a non-transparent government run by radical clerics doesn't get their hands on weapons of mass destruction

President Bush

But the BBC's Nick Bryant says this is diplomatic shorthand for a fundamental disagreement, and that it would be hard for the two leaders to see eye to eye on the issue.

Mr Bush said they had talked about the dangers of allowing weapons of mass destruction to fall into the hands of terrorists, and had agreed to "work closely" on the issue.

The US president has named Iran, along with Iraq and North Korea, as part of an "axis of evil" sponsoring terrorism.

President Putin, however, said Russia's cooperation with Iran was limited to energy resources, and would not undermine nuclear non-proliferation efforts.

'Worrying'

Russia is helping Iran to build a nuclear reactor at Bushehr, which the Americans say could help Iran develop weapons-grade plutonium.

There are major differences behind the smiles

The Russian Atomic Energy Ministry has said the plant will begin operating in September 2003.

But Mr Bush said the Russian president shared his concerns about Tehran's aims.

"I worry about Iran and I'm confident that Vladimir Putin worries about Iran, and that was confirmed today," he said.

"We spoke very frankly and honestly about the need to make sure that a non-transparent government run by radical clerics doesn't get their hands on weapons of mass destruction," he added.

'Economic character'

Mr Putin defended his country's programme.

"Our co-operation with Iran is limited to energy, it only has an economic character," he said, adding that the US was building a similar plant in North Korea.

He also said that he was concerned about the development of missile programmes by "Taiwan and some other states".