Russia Tuesday vowed to stand by its ally Iran and resist any attempts to promote an anti-Iranian agenda amid tensions over Tehran's nuclear program. 

Foreign Minister Sergei Lavrov made the comments during a visit to Moscow by his Iranian counterpart Javad Zarif amid a fresh row over access to Iranian sites where past nuclear activity may have occurred. 

The standoff comes as a landmark deal between Iran and world powers brokered in 2015 continues to unravel. 

"We will be doing everything so that no one can destroy these agreements," Lavrov told reporters after face-to-face talks with Zarif. "Washington has no right to punish Iran." 

Moscow's top diplomat said at the start of the talks that Russia would firmly oppose any "attempts to use this situation in order to manipulate the (United Nations) Security Council and to promote an anti-Iranian agenda." 

Zarif, for his part, described developments around the Iranian nuclear deal – formally known as the Joint Comprehensive Plan of Action – "very dangerous." 

Iran committed under the deal to curb its nuclear activities for sanctions relief and other benefits, but it has slowly abandoned its commitments after U.S. President Donald Trump's decision two years ago to renounce the deal and reimpose sanctions. 

Iran's stockpile of enriched uranium is now almost eight times the limit fixed in the accord, according to an IAEA assessment. However, the level of enrichment is still far below what would be needed for a nuclear weapon. 

On Monday, the head of the UN's nuclear watchdog called on Iran to allow prompt access to two sites where past nuclear activity may have occurred. 

UN nuclear watchdog resolution would be 'counterproductive': Iran 

Iran warned Tuesday that a resolution to be proposed at a meeting of the UN's nuclear watchdog urging the country to allow access to two disputed sites would be "counterproductive."

Reacting to a resolution expected to be tabled by European states at this week's Board of Governors' meeting of the IAEA, Iran's UN Ambassador in Vienna Kazem Gharibabadi said: "Introduction of this resolution aiming to call on Iran to cooperate with the Agency ... is disappointing and absolutely counterproductive." 

Gharib Abadi warned that if the resolution was adopted "Iran would have no choice but to take appropriate measures, the consequences of which would be upon the sponsors of such political and destructive approaches." He did not specify what these measures would be. 

Even though the sites in question are not thought to be directly relevant to Iran's current activities, the agency says it needs to know if activities going back almost two decades have been properly declared and all materials accounted for. 

(With input from AFP)