Russia has sent two nuclear-capable strategic bombers to patrol the western borders of ally Belarus, the authorities in Minsk say, amid heightened tensions across Eastern Europe.
The two Tu-22M3 bombers were accompanied by Su-30SM fighter jets from both the Russian and Belarusian air forces.
It was the third such mission in the area in the last month.
Tensions between Russia and the West have been heightened by a buildup of Russian troops in the region near the country's border with Ukraine.
At the same time, Belarus's relations with the European Union are strained over a migrant crisis along its western border that the EU says was instigated intentionally by Minsk.
Officials in Kyiv have expressed fears that Moscow could use Belarusian territory to support an attack on Ukraine.
The United States and NATO have warned of "massive consequences" if Russia attacks Ukraine.
However, British Defense Secretary Ben Wallace told the Spectator magazine on December 18 that it was "highly unlikely" NATO members would send troops to defend Ukraine from a Russian attack.
"It is not a member of NATO, so it is highly unlikely that anyone is going to send troops to Ukraine to challenge Russia," Wallace said. "We shouldn't kid people we would. The Ukrainians are aware of that."
Wallace added that Britain would continue helping Ukraine build up its own defense capabilities and again warned Moscow of "severe economic sanctions" -- including Russia's possible exclusion from the SWIFT international payments network -- if it attacked Ukraine.
Meanwhile, German Economic Affairs Minister Robert Habeck said in an interview published on December 18 that the Nord Stream 2 gas pipeline to deliver Russian natural gas to Germany could face "severe consequences" in the event of a Russian attack on Ukraine.
He added that "nothing can be excluded" if "there is a new violation of the territorial integrity" of Ukraine.
Habeck also said that "from the geopolitical point of view, the pipeline was a mistake."
Moscow and Kyiv have been at odds since 2014, when Russia seized the Ukrainian region of Crimea and began providing military, political, and economic support to separatist formations in parts of eastern Ukraine.
Moscow denies direct involvement in the conflict in eastern Ukraine, despite compelling evidence to the contrary.
Western analysts say Russia currently has about 100,000 troops positioned near its border with Ukraine.