U.S. media reports of a Russian bounty program to kill U.S. soldiers in Afghanistan are a “downright lie,” Moscow’s ambassador in Washington said Wednesday, and are “poisoning the atmosphere of cooperation” on Afghan peace between the two countries.

“No concrete evidence has been presented” of allegations that a Russian military intelligence unit offered to pay Taliban-linked militants to target American and other coalition forces, Anatoly Antonov said. Authors of the reports are “trying to create an impression that our country is an enemy of the United States.”

But beyond Afghanistan, he said, overall U.S.-Russia relations are in a “deplorable state,” which he attributed largely to U.S. withdrawal from multilateral arms control treaties and refusal to extend or seriously renegotiate the bilateral New START nuclear arms reduction treaty that expires in February.

“It would be no exaggeration to say that arms control issues have always been a core of the U.S.-Russia relations,” he said. “We are deeply concerned about the United States actions leading to the collapse of strategic stability.”

Antonov spoke in a virtual discussion with the Center for the National Interest, a Washington think tank. Now in his third year as ambassador, after serving as Russia’s deputy minister of both foreign affairs and defense, his remarks echoed many of those previously made by Russian President Vladimir Putin in recent months.

While he characterized conversations between Putin and President Trump, including five telephone calls in late March and April, as constructive, Antonov said that “unfortunately, it is not always possible to implement in practice the constructive tone of the presidents’ talks.”

U.S. critics of Trump have long accused him of kowtowing to Putin, and even some inside the administration have expressed concern that Trump has been unable or unwilling to stand up to the Russian leader.

Trump and Putin are not known to have spoken since allegations of the Russian bounty program surfaced. Trump has called the reports a “hoax.”

On other issues, Antonov said that Russia, which has a veto in the U.N. Security Council, will oppose U.S. efforts there to reimpose sanctions on Iran’s sale or purchase of weapons that are to be lifted in October as part of the Iran nuclear deal.

Antonov repeated Russia’s contention, shared by others party to the Iran agreement, that Trump’s decision to withdraw from the agreement more than two years ago “means that the United States has not any right to trigger or to start ‘snapback,’ ” as the reimposition of sanctions is known.

“We can’t see any legal and technical ways for such a decision,” he said.

Antonov declined to be drawn into current U.S. domestic political tensions. “Of course I am shocked. Shocked [by] what I see today in the United States,” he said. But “I have to be very cautious. I am the ambassador of a foreign country.”

Much of his remarks focused on arms control, and particularly a meeting in Vienna last month between newly appointed U.S. special envoy Marshall S. Billingslea and Sergei Ryabkov, Russia’s deputy foreign minister, to discuss New START. Neither side reported progress.

The Trump administration has said that China, with only a small fraction of the intercontinental weapons possessed by the United States and Russia, should be part of any new treaty, and invited the Chinese to the talks over Russian objections. China declined, saying it would be happy to talk with the United States if Washington wanted to decrease its warheads to “parity” with Beijing’s.

“The Chinese factor was in the center of discussion in Vienna between our delegations,” Antonov said. “Frankly, to my regret, Washington has de facto taken the START treaty hostage by insisting” on making it a trilateral accord.