Police officers were believed to be the target of a bomb which left at least 13 people dead in the Pakistani capital, Islamabad.
Dozens of people were injured in the explosion, in a restaurant/hotel near the controversial Red Mosque.
Police officers were quickly on the scene, scouring the blast site for evidence.
Rescuers scrambled to find survivors in the wreckage of the destroyed building.
Earlier, students had returned to the mosque - where, in early July, a stand-off with troops ended in a bloody climax - and remembered those who died there.
Some of the students were vocal in their demands to reinstate the mosque's surviving pro-Taleban cleric, Abdul Aziz.
Hundreds gathered as protesters daubed graffiti and red paint on the dome of the mosque, which authorities had repainted in pale colours.
The demonstrations turned to clashes with police. Soon after the unrest was subdued with tear gas, the calm was shattered again by the bomb blast.