KARACHI, Pakistan

At least 25 people were injured in an explosion in the Pakistani garrison city of Rawalpindi on Sunday, according to police.

The explosion believed to have been caused by a grenade blast occurred near a police station, broadcaster Dawn News reported, citing police.

Some are critically wounded in the blast in Punjab state, near the capital Islamabad.

City police chief Mohammad Ahsan told reporters that the nature of the blast is yet to be known.

This was the second bomb blast near a police station in Rawalpindi this month. On Dec.4, at least one person was killed and another seven injured when an improvised explosive device went off outside a police station located in a densely populated locality in the garrison city, which houses the headquarters of the country's powerful army.

No group has yet claimed the responsibility for the attack, a rare happening in this part of the South Asian nuclear state.