A car-bomb attack on a mosque at a police compound in north-western Pakistan has killed at least 21 people and injured more than 100, officials say.

The attack, which killed at least two dozen people and went on for hours, is the latest example of the worsening violence near the Afghan border.

A local militant group, Ittehad-ul-Mujahideen Pakistan, a faction linked to Tehreek-e-Taliban Pakistan, has claimed responsibility for the attack, the news agency reported.