Tehran notified the International Atomic Energy Agency (IAEA) earlier in January that it plans to install more modern equipment at the Natanz site in central Iran, which has previously enriched uranium to 5 percent purity.
That has caused concern because the new gas centrifuges might allow Iran to refine large amounts of uranium to higher levels of purity, which would be suitable for a nuclear bomb, rather than fuel for an atomic power plant or other peaceful uses.
"The IAEA has been notified, and the IAEA will be there and will supervise this, but I'd like to repeat that this is a legal aspect of the matter, while the political aspect is that we, along with the other Security Council members, have called on Iran to freeze enrichment operations during the negotiations," Lavrov told reporters in Moscow.
"But they are doing everything in line with their commitments under the Safeguards Agreement," he added. The Safeguards Agreement between the IAEA and Iran was signed in 1974, and sets out safety measures covering Tehran's nuclear activity.
The Iranian move comes despite international sanctions aimed at slowing Tehran’s nuclear program and amid international efforts to launch a new round of talks between Iran and the "sextet” of international mediators, comprising Britain, China, France, Russia, the United States and Germany.
The group, known as P5+1, held three rounds of talks over the Iranian nuclear issue last year, following a one-year break in the negotiations.
These talks, however, did not result in a breakthrough, as the sides cannot agree on the true nature of Tehran’s nuclear ambitions.
The European External Action Service (EEAS) has recently invited Iran to hold a new round of talks on its controversial nuclear program in February.
The United States, Israel and some of their allies accuse Iran of using its nuclear energy program to build nuclear weapons.
Iran rejects these allegations, arguing as a signatory to the nuclear Non-Proliferation Treaty and member of the International Atomic Energy Agency, it is entitled to develop and acquire nuclear technology for peaceful purposes.
Russia has repeatedly expressed concern over the slow pace of the nuclear talks with Iran, and stressed the need for the new meeting to be held as soon as possible.