The push into Mingora is seen as a key phase of an offensive aimed at crushing the militants, whose influence extends across a wide area of the north-west.

The military says the city is surrounded, most of the militants' ammunition dumps are destroyed and their supply routes cut off.

Nearly 1.5 million people have been displaced by this month's fighting in the north-western region, and about two million since last August, the United Nations refugee agency says.

On Friday, the UN appealed for $543m in humanitarian aid to help those displaced by the conflict.