Ukrainian soccer champion Shakhtar Donetsk says its club headquarters has been occupied by "armed men" as fighting between government troops and separatists continues.

Shakhtar did not identify the men and said the "circumstances of what has happened are being investigated."

The city of Donetsk is the largest under the control of pro-Russian rebels, and has been the scene of fighting between them and Ukrainian troops in recent weeks.

Shakhtar's stadium, the Donbass Arena, suffered largely cosmetic damage from a mortar round last month.

The club's training base was hit by two shells early Saturday, starting a fire which severely damaged the main building.

Shakhtar is playing its home games this season in the western Ukrainian city of Lviv.