An explosion hit a bus carrying paramilitary troops in northwestern Pakistan on Monday, killing at least five soldiers and wounding six others, police said.

The cause of the blast was not immediately known, but a police official said it appeared to be a homemade bomb. The official declined to identify himself as he was unauthorized to speak to the media.

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The explosion occurred in Dir, a rugged district about 130 kilometers (80 miles) northeast of the provincial capital, Peshawar, police official Pervez Khan said.

The troops were traveling to Chitral, a town near Dir, to provide security for an annual polo tournament there, Khan said.

Police cordoned off the scene of the blast as senior security officials investigated what may have caused the explosion.

The military had no immediate details on the blast.

The region has not been known for terrorist attacks, but it is near tribal-dominated northwestern areas of the country bordering Afghanistan where pro-Taliban militants and security forces have battled for more than four years.