"In line with the parliament law, the president ordered work to resume (at the Natanz enrichment facility)," said Javad Vaidi, a member of Iran's Supreme National Security Council.
Mr Vaidi said it was "unacceptable" for Iran to halt its research on enrichment, a process which makes reactor fuel but can be extended to make the core of a nuclear weapon.
Russian talks will go ahead
But Mr Vaidi also said an Iranian delegation will head to Russia on February 20 for talks on a compromise proposal which could help resolve Tehran's nuclear standoff with the West.
The two sides had been expected to hold talks on Thursday to develop a Russian government proposal that would see uranium enriched on Russian soil and transported to Iran for use, but Iran pulled out of the talks.
Russia's idea guaranteed Iranian access to nuclear fuel needed to generate electricity but at the same time prevented the country from developing fuel cycle technology by itself and therefore the capacity to make a bomb.
Japan offers mediation
Meanwhile, Japan has said that it will its warm ties with Iran to try to persuade it to stop its nuclear drive when the Islamic republic's foreign minister visits this month.
Japan, which has invested billions of dollars in Iran's oil industry, said it could mediate between Iran and Western countries and help them step back from growing confrontation.
"Our country, which maintains friendly relations with Iran, will see to it that Iran, which wields influence in the field of energy, will not be isolated in the international community," Chief Cabinet Secretary Shinzo Abe said.
Iranian Foreign Minister Manouchehr Mottaki, who served as ambassador to Japan from 1995 to 1999, will begin a three-day visit to Japan on February 27 that will include talks with his counterpart Taro Aso, the Japanese foreign ministry said.
"Japan's dependence on Iran for oil is high," he said. "It is a great matter of interest for Japan to prevent trouble there." Mr Aso said in a separate news conference.
The United Nations nuclear watchdog, the International Atomic Energy Agency (IAEA), will issue a report on the Iranian activity at its meeting in March.
The UN Security Council is then expected to consider taking steps, including possible sanctions, against Iran.