Richard Drew, File, Associated Press
In this Tuesday, May 4, 2010 file photo, Sergei Ryabkov, Deputy Foreign Minister of the Russian Federation, addresses the Nuclear Nonproliferation Treaty (NPT) conference at United Nations headquarters. Ryabkov, a senior Russian diplomat, accused the U.S. administration on Friday, Feb. 27, 2015 of taking a "destructive" stance in bilateral relations and warned that Moscow could retaliate.

MOSCOW — A senior Russian diplomat on Friday accused the U.S. administration of taking a "destructive" stance in bilateral relations and warned that Moscow could deal "painful" counterblows.

Deputy Foreign Minister Sergei Ryabkov said that Secretary of State John Kerry breached "diplomatic ethics" when he told U.S. lawmakers earlier this week that Russian officials had lied to him about support for separatists in eastern Ukraine. Ryabkov added in remarks carried by Russian news agencies that Washington "lacks moral right" to make such judgment.

Ukraine and the West have accused Russia of backing the rebels with troops and weapons. Moscow denies that, and Ryabkov again dismissed the U.S. accusations as "absolutely unfounded" and "unacceptable."

He warned that Moscow could retaliate to potential new U.S. sanctions, but wouldn't necessarily make them public.

"We are working on them, but it would be wrong to announce them in advance, and, in fact, announce some of them at all," Ryabkov said. "We are leaving all options for ourselves. We have used and, if necessary, will use quite painful countermeasures."

"Our bilateral agenda with the United States has become utterly negative because of the destructive course taken by Washington," Ryabkov said, adding that there are few issues on which Moscow and Washington could still cooperate.

He said that the Iranian nuclear talks remained one of those areas and voiced hope that an agreement could be reached before a March 31 deadline.

The U.S. and Iran have reported progress on a deal that would clamp down on Tehran's nuclear activities for at least 10 years but then slowly ease restrictions on programs that could be used to make atomic arms.

Ryabkov said the latest round of talks has proven that "a chance for reaching agreement on time far exceed the probability of a failure or a delay."

He said that once U.N. sanctions against Iran are lifted, Moscow expects to expand its military and nuclear cooperation with Iran. Russia, which built Iran's first nuclear power plant in the southern port of Bushehr, signed a deal last November to build two more reactors, which would be possibly followed by another six.