Ukraine has closed its airspace to Syria-bound Russian planes with humanitarian aid, Ukrainian Prime Minister Arseniy Yatsenyuk said Thursday, RIA Novosti reports.

Yatsenyuk said during a meeting with his Slovak counterpart Robert Fico that Ukraine would not let Russian aircraft with humanitarian supplies to war-torn Syria use the country’s airspace.

He said that he ordered a Ukrainian state company that services the country’s airtraffic to strengthen control over any flights of Russian aircraft to Syria.