MOSCOW- Russian traders, analysts and industry players today questioned Moscow's announcement that a long-heralded oil-for-assets barter deal with Iran was already being implemented, saying they saw no signs of extra trade.

Russian officials said on Monday Russia was sending grain, equipment and construction materials to Iran in the barter deal, the first step in securing a foothold in a new market since the West imposed sanctions on Russia over Ukraine.

On Tuesday, the Kremlin confirmed the deal was being implemented.

The announcement and an accompanying one that Iran was ready to supply an advanced S-300 anti-missile system to Tehran, prompted alarm in Washington, which, along with other Western countries and the United Nations, has imposed sanctions on Iran over its disputed nuclear program.

Politically sensitive negotiations are now in their final stages on a deal to end a decades-old dispute between Iran and the United States, Britain, France, Russia, China and Germany on the nuclear program, which the West suspects has military aims and Tehran says is peaceful.

Russia has acted quickly to cement ties with Iran after an interim deal was reached this month on curbing the Islamic republic's nuclear program in exchange for removing economic sanctions. Talks will resume on April 21 with the aim of reaching a final accord by the end of June.

A precise mechanism and timetable for lifting sanctions against Iran is still to be worked out. Russia says an arms embargo on Tehran should also be lifted once the final nuclear deal is in place.

On Tuesday, German Foreign Minister Frank-Walter Steinmeier said of the missile plan that it was too early to be giving out rewards.