WASHINGTON, April 13. /TASS/.  The United States is concerned over Russia's possible deliveries of S-300 air defense missile systems to Iran in connection with Tehran's actions in the region, although such developments would not violate sanctions imposed against the Islamic Republic by the UN Security Council, US State Department spokeswoman Marie Harf has said.

Harf’s comment followed reports that Russian President Vladimir Putin signed a decree to lift the ban on S-300 deliveries to Tehran.

However, she said the US believes such step on the part of Russia would be unconstructive.

Lavrov explains why ban was lifted

Russian Foreign Minister Sergey Lavrov said Monday Russia’s voluntary embargo on deliveries of S-300 missile systems to Iran is no longer needed due to progress in the resolution of the situation around Iran’s nuclear program.

"Initially, the decision to suspend the implementation of the contract, which was already signed and came into force, was made in September 2010," he recalled. "It was done in the interests of support for consolidated efforts of the six international negotiators to stimulate a maximally constructive process of talks on settlement of the situation around Iran’s nuclear program."

The minister particularly stressed that "it was done absolutely voluntarily."

"Resolution 1929 of the Security Council, which was approved in 2010, just like any other UN resolutions did not impose any restrictions on deliveries of air defense weapons to Iran. I will emphasize, it was done in the spirit of goodwill to stimulate progress at the talks," he said.

This year, Lavrov continued, the six international negotiators, after a regular round of talks with Iran, "stated" on April 2 in Lausanne "substantial progress in settling Iran’s nuclear problem."

"The P5+1 stated progress in the settlement of Iran’s nuclear program. Political frameworks of the final agreement were coordinated. They received a high assessment everywhere on the international arena," he said.

The P5+1 is the five permanent members of the UN Security Council - the United States, Russia, China, the United Kingdom, and France - plus Germany.

"This result was in many respects achieved because the six international negotiators worked in a consolidated manner on political settlement of the serious problem," he said. "We are convinced that at this stage, there’s no more need of such an embargo, Russia’s separate voluntary embargo."

"S-300 is an air defense missile system, which is of a purely defensive nature. It is not designed for attacks and will not put at risk the security of any regional state, including Israel, of course," Lavrov said.

"Meanwhile, for Iran, taking into account the very tense situation in the region surrounding it, modern air defense systems are very important," he said.

"This is in particular proven by an alarmingly fast development of events in the past week of the military situation around Yemen. Of course, we couldn’t but take into account commercial and reputational aspects too. As a result of contract suspension, Russia did not receive large sums we were to have received," Lavrov said.

"We see no more necessity in doing that, taking into account progress in the talks on settlement of the Iranian nuclear program and an absolutely legitimate nature of this forthcoming deal," he said.

Prospective deal in Iran-P5+1 talks

Iran says it needs nuclear power to generate electricity, but Western powers led by the United States claim Tehran's eventual aim is to create nuclear weapons.

At a meeting in Vienna in November 2014, the P5+1 and Tehran agreed to extend the deadline for a deal in the talks on Iran’s nuclear program to June 30, 2015.

The latest round of talks between Iran and the P5+1 in Lausanne, Switzerland, ended April 2 with the conclusion of a joint comprehensive action plan on the Iranian nuclear program, to be adopted by June 30.

As the plan is being implemented, all political and economic sanctions are to be lifted from Tehran. Meanwhile, on April 9 media quoted Iranian President Hassan Rouhani as saying that if sanctions are not lifted first, Iran will not sign the nuclear deal with the six international negotiators.