Russia paved the way on Monday for missile system deliveries to Iran and started an oil-for-goods swap, signaling that Moscow may have a head-start in the race to benefit from an eventual lifting of sanctions on Tehran.
The moves come after world powers, including Russia, reached an interim deal with Iran this month on curbing its nuclear program.
The Kremlin said President Vladimir Putin signed a decree ending a self-imposed ban on delivering the S-300 anti-missile rocket system to Iran, removing a major irritant between the two countries after Moscow canceled a corresponding contract in 2010 under pressure from the West.
A senior government official said separately that Russia has started supplying grain, equipment and construction materials to Iran in exchange for crude oil under a barter deal.
Sources told Reuters more than a year ago that a deal worth up to $20 billion was being discussed and would involve Russia buying up to 500,000 barrels of Iranian oil a day.
Officials from the two countries have issued contradictory statements since then on whether a deal has been signed, but Russian Deputy Foreign Minister Sergei Ryabkov said on Monday one was already being implemented.
"I wanted to draw your attention to the rolling out of the oil-for-goods deal, which is on a very significant scale," Ryabkov told a briefing with members of the upper house of parliament on the talks with Iran.