Despite a pattern of contrary statements, the United Nations draft resolution on Iranian sanctions will not prevent Russia from moving forward with the controversial sale of S-300 missiles to Tehran, an intelligence expert told Xinhua on Friday.

"Surface-to-air missiles, like the S-300, can really only be used for defensive purposes and I think that's the logic behind not including them in this arms embargo," said Greg Thielmann, a senior fellow at the Washington-based Arms Control Association.

While the draft resolution -- introduced by the United States among the 15-nation Council on Tuesday -- calls on states to block the sales or transfers of weapons, including battle tanks, armored combat vehicles, and missiles or missile systems, it falls short of covering the ban to defensive-only types of weaponry.

"The new sanctions would bring in weapons systems that had not been featured in earlier sanctions but all of those systems are capable of being part of aggressive action against other countries, " Thielmann said.

The S-300, on the other hand, is designed with a defensive application to shoot down attacking aircraft or cruise missiles.

The draft resolution's inclusion of new types of weaponry has created confusion during the past week over whether the ban extends to the S-300. AFP had previously reported that "the supply of the S-300 would indeed be prohibited by this text, if it is adopted in its current form," which was sourced to a Western diplomat who spoke on condition of anonymity.

However, Mikhail Margelov, the head of the Russian Foreign Affairs Committee at the Federation Council, later told reporters that sanctions would not affect the sale.

"As far as Russian economic interests are concerned, this draft does not deal a blow to current contracts existing between Russia and Iran," he was quoted as saying by the Interfax news agency.

Meanwhile, the draft resolution does call on UN members to show "vigilance and restraint" on arms sales, something Russia has demonstrated by repeatedly delaying the 800-million-U.S.-dollar sale.

Russia has blamed the delay on technical difficulties, but Iran had accused Moscow of giving in to the demands of Western countries which accuse Tehran of weaponizing its nuclear program.

"The Russians are in a somewhat delicate position since they had already been contracted to sell these systems," Thielmann said. "And now obviously, if they don't deliver them, the Iranians will accuse them of breaking the contract."