Hasan Ruhani, who handles Iran's nuclear affairs, told Russian President Vladimir Putin that the Islamic republic had agreed to the UN nuclear watchdog's conditions.
"Before your government I officially announce that today we are giving to the IAEA (International Atomic Energy Agency) a letter agreeing with the additional protocol.
From today we are temporarily suspending our process of uranium enrichment," Ruhani, the head of Iran's Supreme National Security Council, told Putin.
The halting of uranium enrichment, a process to create material that can be used to make an atomic bomb, is one of a number of demands set by the IAEA for Iran to allay fears about its nuclear activities.
At a meeting with IAEA chief Muhammad ElBaradai on Saturday, Ruhani had promised to hand over the letters accepting the UN body's demands.
"They (the IAEA) gave us to understand that they had no further questions that Iran had not already answered," added Ruhani at his Kremlin meeting with Putin.
Putin responded that Iran had a right to a uranium enrichment programme, but was happy to hear news that it was being suspended.
"With regard to the enrichment of uranium, Iran has a right to carry out these kinds of activities but we note with pleasure that Iran has itself resolved to limit itself," Putin said.
Putin says Iran has a right to a nuclear programme
By signing the key additional protocol to the Non-Proliferation Treaty, Iran allows snap inspections of its nuclear sites.
It would be a major step forward to solving a months-long standoff with the IAEA over its nuclear programme.
Despite US accusations that Iran is seeking to develop nuclear weapons, Russia is helping Tehran build an $800 million nuclear reactor in Bushehr. Iran says its atomic programme is entirely peaceful.
Putin added, "I do not see any obstacles to cooperating with Iran in the nuclear sphere."