Russian Atomic Energy Minister Alexander Rumyantsev said that the Iranian side had been "too busy" with preparing documents for the International Atomic Energy Agency (IAEA) on its nuclear program to work on the agreement for the Bushehr power reactor.
Russia has said it would not deliver any fuel for the Bushehr reactor until Tehran signs the agreement, under which it would agree to return all of the reactor's spent fuel back to Russia.
"Fuel will not be needed at Bushehr for a while, deliveries will not begin until next year, so we have at least three months to prepare to sign the agreement," Rumyantsev told the ITAR-TASS news agency.
Russia has been building the Bushehr reactor over strong objections from the United States and Israel who fear that Tehran could use it as a front for a nuclear weapons program.
Rumyantsev's comments came a day before IAEA, the Vienna-based UN nuclear watchdog, is due to meet to discuss Iran's nuclear programme, amid US allegations that the clerical regime's bid to generate atomic energy is merely a cover for nuclear weapons development.
Iran last month agreed to meet a raft of IAEA demands including the suspension of uranium enrichment, but insists that its pledge to suspend its controversial work on the sensitive nuclear fuel cycle is voluntary and temporary and could be reversed at any time.
On Wednesday, Iran's top national security official said Tehran would refuse any further IAEA demands to halt its uranium enrichment activities.
"We have said clearly that any phrase in a resolution aimed at transforming the voluntary pledge by Iran to suspend uranium enrichment into a legal obligation will be unacceptable to us," the secretary of Iran's Supreme National Security Council, Hassan Rowhani, was quoted as saying by the official news agency IRNA.