Turkey has closed its airspace to Russian civilian and military planes flying to Syria, Turkish Foreign Minister Mevlut Cavusoglu was quoted as saying Saturday by local media.

The announcement marks one of the strongest responses to date by Turkey, which has cultivated close ties with Moscow despite being a member of the NATO defense alliance, to Russia’s two-month military assault on Ukraine.

“We closed the airspace to Russia’s military planes — and even civilian ones — flying to Syria. They had until April, and we asked in March,” Turkish media quoted Cavusoglu as saying.