Ukraine's Interior Minister says four civilians and three police officers have been wounded in an attack by armed men whose weapons include grenades in a western city.

Arsen Avakov says that the armed group has been surrounded by police in the city of Mukhachevo. He says the group has seized a "civilian object," but local news websites have described it as a sports club.

The local reports say Saturday's attack has been carried out by men bearing the insignia of the far-right nationalist militia Right Sector and that the sports club, which includes a gym and a pool, is owned by a national parliament member from a faction that opposes Right Sector.

Mukhachevo is in far western Ukraine, near the border with Poland and Slovakia.