RANGOON—Kachin ethnic rebels battling the army in northern Burma say they have shot down a government helicopter, but the army says it crashed due to engine failure.

An emailed announcement from the Kachin guerrillas says they shot down the helicopter late on Friday as heavy fighting raged.

A senior government official citing military sources said Saturday tan Mi-35 helicopter crashed in Kachin-controlled territory due to engine failure. He spoke on condition of anonymity because he is not authorized to divulge military information.

The Kachin have long sought greater autonomy from the central government. Intermittent fighting escalated last month when the rebels rejected a government demand that they allow supply convoys to reach an army base.