Russia annexed Crimea from Ukraine in 2014 and used it as a launchpad for the invasion of its neighbour in February.
One person has been killed following a series of blasts at a Russian military air base close to seaside resorts on the annexed Crimean peninsula.
Witnesses said they heard at least 12 explosions at about 3.20pm local time (1.20pm BST) from the Saky base on the west coast.
