(Reuters) - Britain's defence ministry said on Saturday that Russian air activity remains high over Ukraine's Donbas region with Russian aircraft carrying out strikes using both guided and unguided munitions.

       "The increased use of unguided munitions has led to the widespread destruction of built-up areas in the Donbas and has almost certainly caused substantial collateral damage and civilian casualties," the ministry said in a tweet.

       It said Russia increased its use of tactical air to support its creeping advance, combining air strikes and massed artillery attacks to bring its firepower to bear as its operational focus has switched to the Donbas.

       (Reporting by Maria Ponnezhath in Bengaluru; Editing by Mark Heinrich)