A Russian foreign ministry official said on Friday that Belarus may enter the conflict in Ukraine if Kyiv decides to "invade" either country.
Russia used Belarus as a springboard to invade Ukraine in February 2022, and since October has deployed troops in Belarus for joint military drills.
Both countries have since agreed to intensify their military co-operation, raising fears Moscow could use its close ally to launch a new offensive on Ukraine from the north.
In an interview with state media, foreign ministry official Aleksey Polishchuk said that Russia's joint drills with Belarus were designed to prevent escalation, but warned that Belarus may join the Ukraine conflict if it or Russia were invaded.
"From a legal point of view, the use of military force by the Kyiv regime or the invasion of the territory of Belarus or Russia by the armed forces of Ukraine are sufficient grounds for a collective response," Polishchuk told the TASS news agency.
He added, however, that it was up to the leaders of the two countries whether they would make that decision.
Ukrainian President Volodymyr Zelenskiy said on Wednesday that his country must "be ready" at its border with Belarus, but that he so far only saw "powerful statements" coming from his neighbor.
"We understand that apart from powerful statements, we do not see anything powerful there, but nevertheless we must be ready both at the border and in the regions," he said.
