US President Barack Obama said Friday he was not surprised that Russia lifted its ban on supplying missile systems to Iran, despite the move coming at the height of intense international talks on Tehran's nuclear program.

President Vladimir Putin, whose own government is under strict economic sanctions for Russia's involvement in unrest in Crimea and Ukraine, earlier this week removed the ban on supplying Iran with sophisticated S-300 air defense missile systems.

The move triggered concern that such sales could embolden Tehran in talks with the West on curbing its nuclear program.

"I'm not surprised, given some of the deterioration in the relationship between Russia and the United States, and the fact that their economy's under strain and this was a substantial sale," Obama said at a joint press conference in the White House with Italian Prime Minister Matteo Renzi.

"This is a sale that was slated to happen in 2009, when I first met with then-prime minister Putin. They actually stopped the sale, paused or suspended the sale, at our request," Obama added.

"And I'm frankly surprised that it held this long, given that they were not prohibited by sanctions from selling these defensive weapons."

On Thursday, the White House had suggested that economic desperation may have driven Moscow to lift the ban.

The move has infuriated some US lawmakers, who warned it could escalate tensions just as international powers -- including Russia -- seek to finalize an accord with Iran that would severely restrict its nuclear program and prevent it from developing an atomic bomb.

Obama warned against congressional moves to "just slap on even more sanctions" on Iran, arguing that the reason they have worked is that Washington "painstakingly" built an international sanctions coalition that has held for years.