(Reuters) – A senior Russian diplomat, in an interview published on Thursday, urged the United States to pay attention to discussions under way on possibly altering Moscow’s nuclear doctrine to suit changed conditions in international relations.

Deputy Foreign Minister Sergei Ryabkov, interviewed by the Izvestia media outlet, also said Moscow did not rule out downgrading diplomatic relations with certain Western countries if they failed to alter their “Russophobic” approach to ties.

Ryabkov restated Kremlin leader Vladimir Putin’s assertions of recent weeks that Russia’s nuclear doctrine, setting down when such weapons could be used, was being reassessed.

He told Izvestia that the doctrine was drafted “in a different era and in different circumstances” and that he hoped the discussions now “are being taken seriously by our opponents”.

“I am not anticipating the outcome, but I urge our adversaries to think about what the president is saying,” he said.

“They are literally playing with fire … and must learn not to indulge in dangerous illusions, but to try to look at the world soberly and understand that we have immutable national interests which we are prepared to defend to the end,” he said.

The doctrine states Russia may use nuclear weapons in response to a nuclear attack or in the event of a conventional attack that poses an existential threat to Russia.

Putin said this month that Russia had no need to use nuclear arms to secure victory in Ukraine, the strongest signal to date that the conflict would not escalate into nuclear war.

In his comments to Izvestia, Ryabkov said Russia had never initiated a downgrade in relations with any country “despite all the vicissitudes of the most difficult phase in our relations with the so-called collective West.

“We believe that embassies and the work of ambassadors are a particularly difficult job in the current circumstances and they should not be neglected,” he said. “We do not rule out any options in the future. Everything will depend on how our adversaries conduct themselves.”

Ryabkov also said he believed no progress had been made in arranging an exchange of detainees, including U.S. journalist Evan Gershkovich, who went on trial on spying charges on Wednesday in the Urals city of Yekaterinburg.

“As far as I know, for the moment, no. The Americans must again and again carefully consider the ideas expressed in the appropriate channels from our side,” he said. “I hope that they will understand in the end the common season and reason on which these proposals were based.”