TEHRAN, Iran – Iranian President Mahmoud Ahmadinejad accused Russia’s president Friday of turning against Tehran and joining the United States in spreading lies about its nuclear program, in the latest sign that Iran is drifting apart from a one-time key backer.

Ahmadinejad said Dmitry Medvedev entered a “propaganda drama” directed by Washington by saying last week that Iran was getting closer to being able to develop nuclear weapons.

The Iranian president has had harsh words for Moscow since it became apparent that Russia would support last month’s new United Nations sanctions against Tehran for its refusal to stop parts of its nuclear program. In the past, Iran had depended on allies Russia and China — and their veto power at the Security Council — to block tough penalties.

“Russia is a great nation and we are interested in continuing friendship between the two nations but his (Medvedev’s) remarks are part of a propaganda drama that is to be carried out by the U.S. president against the Iranian nation,” Ahmadinejad said in a speech posted on his website Friday. “In fact, Mr. Medvedev has kick-started this drama,” he said.

Russia is in a difficult position in the international standoff with Iran, in part because it does not want to jeopardize decades of political and trade ties with the country. Still, Moscow has lately shown increasing frustration with Iran, and last month backed the new sanctions.

Iran insists its nuclear work is only for generating power and other peaceful uses. The United States and its allies accuse Iran of using its civilian nuclear program as a cover to develop a nuclear weapons capability.

Medvedev said last week that although Iran is “an active and trusted trading partner … this does not mean we don’t care how it develops its nuclear program and what its military components look like. In this respect we expect explanations from Iran.”

Medvedev also urged Iran to find the courage to cooperate with the international community over its disputed nuclear program.

On Friday, Ahmadinejad answered back, saying Medvedev was joining the United States against Iran and harming Russia’s interests.

Ahmadinejad first delivered unusual criticism of Medvedev in May, accusing him of caving in to U.S. pressure for new sanctions, saying “justifying the behavior of Mr. Medvedev today has become very difficult.”

Russia has a series of energy and weapons contracts with Iran, including a batch of sophisticated S-300 ground-to-air defense missiles.

Last month, the Russian government said the new U.N. sanctions forbid delivering the weapons, while Iranian officials later insisted the sanctions don’t cover contracts signed before the restrictions entered force.

Russia and Iran penned the S-300 agreement in 2007, but their delivery has stalled amid pressure from the West.

Last week, Sergei Chemezov, the head of the state-owned industrial giant Russian Technologies, said the contract had not been annulled pending a decision from the president.

The truck-mounted S-300 missiles can target aircraft, low-flying cruise missiles and ballistic missiles, according to weapons experts.