At least 21 people have been killed in a bomb blast in a market in northern Pakistan.

Some 40 others were wounded in the explosion in the remote Kurram region, which borders Afghanistan.

The Pakistani army says helicopters were being provided to transport the wounded to hospital.

Some reports spoke about a suicide bomber, others say the blast was caused by a homemade device.

Taliban militants have previously been active in the area but there has also been tension between Shiite and Sunni Muslims.