DNIPRO/KYIV, Ukraine, Jan 16 (Reuters) - Russia and Belarus will begin joint air force drills on Monday, which have triggered fears in Kyiv and the West that Moscow could use its ally to launch a new ground offensive in Ukraine. Minsk says the drills are defensive, and since Moscow used its neighbour as a springboard for its invasion of Ukraine last February Belarus has conducted numerous military exercises, both on its own and jointly with Russia.