“Given the potential desperation of President Putin and the Russian leadership, given the setbacks that they’ve faced so far, militarily, none of us can take lightly the threat posed by a potential resort to tactical nuclear weapons or low-yield nuclear weapons,” Mr. Burns said, in answering questions after a speech in Atlanta.
Prominent voices in Russian state media have made increasingly incendiary statements recently, calling for more brutality in battles that have already sparked calls for war-crimes investigations of the Russian forces.
Much remained unclear about Russia’s setback in the western Black Sea, where a blast on Thursday morning — Wednesday night in the United States — and subsequent fire forced many of the Moskva’s roughly 500 crew members to abandon ship. There was no word on casualties. Ukraine said it had struck the vessel with two Neptune missiles and sunk it.
Russia’s Defense Ministry initially said its sailors had managed to put out the fire and the Moskva, commissioned in 1983, remained afloat. But hours later, it said, the ship sank while being towed to port in a storm.
Western defense officials said they could not be sure what caused the explosion aboard the 12,000-ton ship. Three American officials briefed on the incident said all indications were that it had been hit by missiles. The officials cautioned that early battlefield reports can sometimes change, but expressed deep skepticism over the Russian account of an accidental fire.
Ukraine has been stressing the need for coastal defense weapons, and the U.S. announced this week that it would send more of them. Pentagon officials said that other Russian ships had moved farther from the Ukrainian shoreline, lending credence to the claim of missile strikes.
“It’s going to have an impact on their naval capabilities, certainly in the near term,” but the long-term picture is unclear, said the Pentagon spokesman, John F. Kirby, a former Navy rear admiral.