At least 37 people were killed and over 150 wounded when a Moharram procession passing through downtown Quetta in Pakistan's Baluchistan province was attacked by radical Sunnis armed with automatic weapons and grenades on Tuesday, report agencies.

Armed members of the procession returned fire. The casualty figure is likely to mount.

News of the attack led to a violent rampage by the Shia community in the provincial capital, and over 50 shops, houses, a Sunni mosque and the offices of a television network were gutted before the army was called out and curfew imposed.

This was said to be the worst outbreak of sectarian violence in Pakistan since a suicide attack on a Shia mosque in Quetta in July killed more than 50 people. Pakistani officials had then hinted that Indian agents operating from Afghanistan were involved in that attack.