BBC Correspondent Zaffar Abbas

Two bombs have exploded in the heart of Karachi, causing widespread damage to property in the Pakistani city.

Security in the city has been increased and paramilitary troops have been stationed around the provincial assembly buildings and government offices where the explosions took place.

The first bomb exploded inside a newly constructed police check-post near the Sindh provincial assembly building. The blast was so powerful that it destroyed the entire structure of the check-post.

Officials said the police post was not occupied at the time of the explosion and only three passers-by were injured. The second bomb went off in the same area less than an hour later, also causing widespread damage.

Police said it was placed under a car outside the city's main passport office. Several people were injured by the explosion which also damaged more than a dozen cars and a few roadside shops.

Senior officials said the explosives used in both the blasts were identical and were detonated with timing devices. So far no group has claimed responsibility for the explosions.

Officials believe they are part of a campaign to spread fear and terror in a city where rival militant groups have already remained involved in a bloody feud for the past many years.