Ukrainian air defenses shot down five Russian planes and a helicopter in the Luhansk region, Ukraine’s military said Thursday amid reports of a Russian invasion targeting the country.

"In connection with the conduct of anti-terrorist activities, shipping in the Azov Sea is suspended from 4.00 am (0100 GMT) on February 24 until further notice," a representative of the Federal Agency for Maritime Transport Rosmorrechflot told Russian agencies.

"According to the Joint Forces Command, today, Feb. 24, in the area of the Joint Forces operation, five planes and a helicopter of the aggressors were shot down," the army general staff said, referring to the area where clashes with the Russia-backed separatists are ongoing.

The statement came after the Ukrainian side claimed another Russian jet was shot down in eastern Ukraine.

Russia denied the Ukrainian claims and said its military "downgraded" Ukrainian air defenses in high-precision strikes targeting command centers and air bases.