**A loud explosion has hit a security agency building in the northwestern Pakistani city of Peshawar, according to witnesses.**There are reports of casualties, but it is not clear how many are dead or hurt.
The cause of the blast was not immediately clear, but the city has been frequently targeted by militants in recent weeks.
Attacks have increased as the army continues its offensive against the Taliban in South Waziristan region.
More than 100 people were killed in a blast at a city market more than two weeks ago.