Russia has said its long-standing contract to supply surface-to-air missiles to Iran will not be affected by new UN sanctions.
Russia agreed to supply Iran with S-300 systems several years ago but has not delivered them.
Russian Foreign Minister Sergei Lavrov stressed the missiles were not subject to the limits set by the UN on cooperation with Iran.
He said Moscow was in talks on building further nuclear reactors in Iran.
The US and Israel are concerned the S-300 missiles, designed to counter both aircraft and cruise missiles, might be used to protect Iran's nuclear facilities from possible attack.
The UN Security Council voted on Wednesday to impose a fourth round of sanctions on Tehran for failing to halt its nuclear enrichment programme.
Iran insists it wants only atomic energy but a number of Western countries suspect it of trying to build nuclear weapons.
The measures were passed after being watered down during negotiations with Russia and China.
Russian officials pointed out on Thursday that the new UN Security Council resolution affected only "missiles or missile systems as defined for the purpose of the UN Register of Conventional Arms".
The register's section on missiles states that it "does not include ground-to-air missiles".
Speaking on a visit to Uzbekistan on Thursday, Mr Lavrov said: "As far as military-technical cooperation is concerned, the resolution introduces limits to cooperation with Iran on offensive weapons and defensive weapons do not fall under these limits."
Mr Lavrov said Moscow was in talks on building nuclear reactors in Iran in addition to the Bushehr site, due to open in August after years of delay.
"We are practically discussing this now," he told Reuters news agency.
The existence of a missile "loophole" has been attacked by critics of the Obama administration such as John Bolton, former US envoy to the UN, who told the Washington Times it amounted to "diplomatic malpractice".
Republican Senator John McCain was quoted by Reuters as saying the UN resolution was "a lowest common denominator product".
The White House said it welcomed the fact that Russia had, "up to this point", shown "restraint" in not delivering the S-300 to Iran.
"Russia has exercised responsibility, restraint and has not delivered those missiles to Iran," state department spokesman Philip Crowley was quoted as saying by AFP.
Iran's parliament is to reconsider relations with the UN nuclear watchdog following the latest round of UN sanctions, state media says.
The announcement by the national security and foreign policy committee head, Alaeddin Boroujerdi, did not specify what action might be taken.
But correspondents say options could include restricting access by UN inspectors to Iranian nuclear sites.
Iranian President Mahmoud Ahmadinejad said the UN's resolutions were like a "used handkerchief which should be thrown in the dustbin. They are not capable of hurting Iranians".
Iran's two main opposition leaders have reportedly called off demonstrations planned for Saturday to mark the first anniversary of last June's disputed presidential election.
In a statement published on pro-reform website sahamnews.com, Mir Hossein Mousavi and Mehdi Karroubi said the decision had been made to protect lives and property.
The new UN resolution includes measures to prohibit Iran from buying heavy weapons such as missiles and helicopters.
The Security Council voted by 12 votes to two in favour; Brazil and Turkey voted against, while Lebanon abstained.
They argued that the move was counter-productive and endangered a diplomatic solution.
Turkish Prime Minister Recep Tayyip Erdogan said on Thursday that the imposition of the latest sanctions was a "mistake", reports Reuters news agency.
Although the measures were not as tough as the US had wanted, President Barack Obama said they sent an unmistakable message about the determination to stop the spread of nuclear arms.
BBC Middle East editor Jeremy Bowen says the most significant parts of the resolution create a legal basis to restrict the supply of goods that Iran wants for its alleged nuclear missile programmes.
Our correspondent says the measures single out the Iranian Revolutionary Guards, who run much of the economy - including the national shipping line, which Western diplomats say is trying to evade sanctions by setting up front companies.
The resolution toughens rules on financial transactions with Iranian banks, and increases the number of Iranian individuals and companies that are targeted by asset freezes and travel bans.