US President Barack Obama said he is surprised that Russia's suspension of missile sales to Iran "held this long," according to Tass News Agency.

Obama said the sale was initially set to occur in 2009, but Russia put it on hold at the United States' request.

“And I’m frankly surprised that it held this long, given that they were not prohibited by sanctions from selling these defensive weapons,” Obama said at a news conference.

“When I say I’m not surprised, given some of the deterioration in the relationship between Russia and the United States, and the fact that their economy is under strain and this was a substantial sale,” he added.

Russian President Vladimir Putin said on Thursday the sale was resumed because of progress in nuclear talks with Iran.

Putin on Monday signed a decree that lifts a ban on "the shipment from Russia to Iran" of the S-300 missiles.

The decree lifts the ban on transit through the Russian territory, including by air, the delivery from the Russian territory to Iran and the transfer outside of Russia with the use of vessels and aircraft flying the Russian state flag of S-300 missile air defense systems.