Washington has asked Moscow to reconsider selling Iran anti-aircraft missiles as the crisis over its nuclear programme continues.

Russia plans to sell Tehran 29 TOR M1 mobile surface-to-air missile defence systems in a deal said to be worth about 700 million (£392m).

"This is not time for business as usual with the Iranian government," a top US state department official said.

The US also urged other states like China to review defence sales to Iran.

'Wrong time'

"There are a lot of countries that allow the export of dual-use technologies, and the position of the United States is that should be prohibited," said Undersecretary of State Nicholas Burns.

"All countries should refrain from military sales and arm sales."

Speaking about the Russian missiles, he said:

"We hope and we trust that that deal will not go forward because this is not time for business as usual with the Iranian government."

Russia and China are both strongly resisting attempts to impose United Nations sanctions on Iran, which the US and other Western states believes is pursuing nuclear weapons.

The US arms appeal is a sign of increasing concern in Washington at the speed with which Iran is pursuing its programme, the BBC's Jonathan Beale reports from Washington.

New report

Russia says it has to see concrete proof that Iran's nuclear programme - which it is supplying with technology - is not peaceful.