KIEV, June 8 - An explosion which sank a border patrol boat off Ukraine's strategically important port city of Mariupol was caused by a separatist-made bomb, the Ukrainian military said on Monday, Reuters reported.

The boat exploded on Sunday, killing one crew member and wounding five others, as it left its mooring station in Mariupol, which is on the Sea of Azov and on the edge of the conflict between Ukrainian forces and Russian-backed separatists.

"The explosion of the patrol boat in the Azov Sea was caused by a rebel homemade bomb," the military said in a statement.