© Ministry of defence of the Russian Federation / A Tupolev Tu-22 M3 strategic bomber of the Russian Aerospace Force
"There is no reason to suspect Russia of violating UN Security Council resolution 2231 [on the sale and transfer of arms to Iran]," Lavrov told a news conference on Wednesday.
He said that "under the resolution, the UN Security Council sanctions deliveries, sales and transfers of specific types of arms to Iran, including combat aircraft," while the Russian deployment involves no such moves.
Comment: Iran has clarified matters, pointing out that Russia is only using the base for refueling. There are no Russian troops stationed at the base, according to Alaeddin Boroujerdi, the head of the Iranian parliament's National Security and Foreign Policy Committee. Moreover, the Iranian constitution bans any foreign nations from having a military base in Iran.
"These military aircraft are used by air forces after Iran's authorization for taking part in the anti-terrorist operation in Syria after a legitimate request from its government," he said.
On Tuesday, Russian Tu-22M3 long-range bombers conducted the first airstrikes against Islamic State (IS, previously ISIS/ISIL) targets in Syria flying from the Iranian airbase.
Military experts say the new deployment allows the anti-IS air campaign to be more efficient in terms of saving fuel, thus carrying heavier bomb loads, as opposed to operating from relatively remote air bases in Russia.
"There is absolutely nothing to discuss," Lavrov said, adding that there is no need to look for fault.
"Otherwise, we will have to sort out how a vast amount of cash made it to Iran from the US, and why bank transfers from the US to Iran have taken place in dollars - it is strictly prohibited under American laws."
The US State Department said Russia's deployment was "unfortunate, but not surprising."
"I think we are still trying to assess what exactly they are doing to the extent that they are doing it," spokesman Mark Toner told reporters on Tuesday. Later in the day, the State Department said Washington will examine if the use of the Iranian airbase violates UN resolutions.
On Wednesday, the Russian Defense Ministry issued a statement saying the UN resolution 2231 outlaws the use of combat aircraft "inside Iran," while the Tu-22M3s are used inside Syria, "which is an independent and sovereign state."
"We'd like to have an answer to a simple question - is there any provision in the UN Charter, or a UN Security Council resolution, or a bilateral US-Syria agreement allowing the US to bomb Syrian territory ... from Turkish airbase Incirlik or any other foreign air bases," Major General Igor Konashenkov, spokesman for the ministry, said in turn.
Any western accusations that Russia's use of the Iranian airfield is a violation of the UN sanctions against the country are "absurd," Ivan Eland, US defence analyst and author, told RT.
The harsh rhetoric is explained by the fact that the move "is perceived as Russia getting more of an advantage in the Middle East. And that's always been a US playground," he said.
"The accusations that Russian is violating sanctions [against Iran] are kind of absurd on its face. I'm not a lawyer, but even if there's a violation - that's a technical violation. But I think it's not a violation at all because the Russians aren't supplying, selling or transferring any weapons, which is what the UN resolution says, to the Iranians," Eland explained.
"In the US, we're still in some respects fighting the Cold War, even though we don't call it that anymore," the expert added.
Comment: More petty meddling from the US... Gosh, you'd think they actually don't want anyone to defeat Daesh and al-Qaeda!