A senior official at the Collective Security Treaty Organization said Wednesday that the Moscow-led military alliance has taken note of rising tensions between Ukraine and Belarus after Kyiv last week threatened to strike military targets inside Belarusian territory.

“We’ve been hearing the Kyiv regime’s recent statements about Belarus,” Viktor Vasilyev, Chairman of the CSTO Permanent Council, said at the St. Petersburg International Legal Forum. “The situation on the border between Ukraine and Belarus is growing more tense.”

His comment follows an ultimatum from Ukrainian President Volodymyr Zelensky, who last week said his military would strike ground stations in Belarus if it continues to allow Russia to use them. The stations, he claimed, were used in recent Russian strikes on Ukraine.

Zelensky warned that if Belarusian President Alexander Lukashenko did not take down the stations, then Ukraine’s military would.

“I think a week will be enough for him to do it. If he doesn’t do it, we will,” Zelensky said in an interview on Ukrainian television.