MOSCOW — A Russian contractor said yesterday that Moscow and Tehran have reached agreement on a schedule for completing construction of a nuclear power plant in southern Iran — a facility that plays a central role in international tensions over Tehran’s nuclear program.

“The difficulties with our Iranian customers have been settled,” an Atomstroiexport spokeswoman, Irina Yesipova, said. She did not specify when the agreement had been reached but said the Russian and Iranian sides “now share a common view of the timetable for construction of the plant, including the delivery of fuel.”

America and other critics have long protested construction of the $1 billion plant in the southern Iranian city of Bushehr, saying it would give Iran cover for developing a nuclear weapons program. Construction has been sporadically delayed amid disputes between Iran and Russia over payment, fuel delivery and other issues. But Russia has remained opposed to a American-led push for international sanctions against Iran for allegedly seeking to develop nuclear weapons.

Russian news agencies cited the head of Atomstroiexport, Sergei Shmatko, as saying details of the timetable for completing the facility would be released later this month.

Mr. Shmatko did not give details of the completion plans, but told ITAR-Tass that fuel would be delivered to Iran about half a year before the plant launches operations.

Although Russia has resisted drives to impose sanctions on Iran, it also repeatedly has urged Tehran to cooperate with the International Atomic Energy Agency to resolve concerns over the nuclear program.

Foreign Minister Sergey Lavrov underlined that position later yesterday after a meeting in Moscow with his Iranian counterpart, Manouchehr Mottaki.

Mr. Lavrov said resolving the controversy is possible “solely on the basis of the nuclear nonproliferation treaty, IAEA rules and principles and, certainly, with Iran proving its right to the peaceful use of nuclear energy,” according to the Interfax news agency. Mr. Lavrov spoke by phone yesterday with Secretary of State Rice about “the continuation of diplomatic efforts on resolving the Iranian nuclear issue,” as well as Kosovo, the Foreign Ministry said. Mr. Shmatko raised the prospect of creating a Russian-Iranian joint venture “to ensure security” at the Bushehr plant, according to the RIA-Novosti agency.

That could indicate Russian interest in ensuring that enriched uranium at the plant is not stolen or diverted. Depleted fuel rods also could be reprocessed into plutonium.