Thirty-five people died and more than 130 were injured when Russian troops launched air strikes on a military training ground outside Ukraine's western city of Lviv, near the border with Poland, local officials have said.
Ukraine said up to 30 missiles were fired.
Russia "launched an air strike on the International Centre for Peacekeeping and Security", the head of the Lviv regional administration, Maksym Kozytsky, said on his verified Facebook page.
"35 people died as a result of the shelling," Kozytsky later wrote on Telegram, updating an initial toll of nine.
"134 more with injuries of varying severity are in a military hospital," he added, saying the information on the toll was still being updated.
Fires at the base have been almost fully extinguished and experts were examining the debris, the governor said.
The military base in Yavoriv, located some 40 kilometres (25 miles) northwest of the city, was a training centre for Ukrainian forces with foreign instructors, including from the United States and Canada.
It was also a hub for joint exercises involving Ukrainian soldiers and NATO allies.
Ukrainian Defence Minister Oleksiy Reznikov said "foreign instructors work here", although it was unclear whether any were present during the attacks.