NOVO OGAREVO: An attack on Iran would be "unacceptable," Russian Prime Minister Vladimir Putin said Friday, but also urged Tehran to show restraint in its controversial nuclear programme.

"This would be very dangerous, unacceptable, this would lead to an explosion of terrorism, increase the influence of extremists and I doubt very much that such strikes would achieve their stated goal," Putin said.

"The Iranians should show restraint in their nuclear programme," he added, speaking at a meeting with foreign Russia experts at his residence outside Moscow.

The United States and Israel have never ruled out the option of carrying out air strikes to prevent Iran from acquiring an atomic bomb.

Tehran denies that its nuclear programme is aimed at building weapons and says it is civilian in nature.