Pakistan's President, Pervez Musharraf, has warned he will take tough action to stop sectarian violence between Sunni and Shi'ite Muslims in the city of Karachi.

A spokesman said Mr Musharraf was gravely concerned about the situation, after yesterday's explosion at a Shi'ite mosque which killed at least 15 people and injured around 40.

Following the blast, vehicles, petrol stations, schools, shops and banks have been set on fire in reprisal attacks.