"They were apparently trapped in the burning building," fire brigade chief Kazim Ali told the BBC News website.

Five people were killed and about 20 others wounded in the suicide attack on the Shia mosque in central Karachi.

There have been numerous acts of sectarian and criminal violence in Karachi in recent years.

Last Friday, a suicide bomber in the capital, Islamabad, killed 19 people and wounded nearly 100 in an attack on a shrine where hundreds of Shias had gathered.

Cars torched

The victims of Monday's mosque bombing included two people believed to have carried out the attack and a policeman.

Several eyewitnesses told us that there were 18 to 20 people inside the KFC when it was set ablaze Kazim Ali Fire chief

Police say they have now identified him as Mohammed Jamil, a resident of Karachi. They say he is a member of the banned Jaish-e-Mohammed militant group.

Soon after the blast angry protesters set fire to a branch of Kentucky Fried Chicken.

Two petrol stations and several cars were also attacked as news of the mosque attack spread.

"We were stopped from reaching the affected area by the protesters," Mr Ali said.

"The mob started to disperse after midnight and it took us another two hours to put out the fire at KFC."

The BBC's Aamer Ahmed Khan in Karachi says the restaurant was attacked because of its proximity to the mosque. KFC outlets, closely identified with the US, are frequently targeted during anti-American riots in Pakistan.

Trapped inside

Firefighters entered the building to discover four charred bodies, two each at the ground and first floors.

Shortly afterwards, two more bodies were recovered from the freezer in the basement.

They had apparently frozen to death.

"Several eyewitnesses told us that there were 18 to 20 people inside the KFC when it was set ablaze," Mr Ali said.

The mosque was attacked when people had started to pray

"Most of them escaped by climbing up to the roof and jumping onto the adjacent building."

The dead were identified as KFC workers.

Karachi police have stepped up security for the funerals of the victims, which are expected to be held on Tuesday.

New security protocols are already being implemented for public areas in general and mosques in particular.

Mosque administrators across the city have been instructed to keep their doors closed during prayers. No vehicles are allowed to be parked around mosques at prayer times, police said.

Religious leader killed

Monday's violence started when three people walked into the mosque and started firing in the air.

Sectarian attacks May 2005: 19 killed and nearly 100 wounded in Islamabad mosque attack March 2005: 43 Shias killed in a bomb blast in Fatehpur, Baluchistan Oct 2004: Car bomb in Multan kills 40 Sunnis Oct 2004: 30 killed in a suicide attack on a Sialkot Shia mosque May 2004: 20 killed in bombing of Shia mosque in Karachi May 2004: 15 die in Karachi Shia mosque attack

"The bomber rushed to the spot where people had gathered to pray, and the next thing we heard was a loud explosion," mosque spokesman Shahzad Rizvi told BBC News.

"In the mayhem I heard the other two attackers begin firing."

Police are hoping to question the injured attacker currently undergoing treatment at a local hospital to find out who was behind the attack.

"He is still unconscious and we haven't had a chance to interrogate him as yet," chief of investigations Manzoor Moghul told the BBC News website.

Separately, the murder of a prominent religious leader on Monday night has also added to the tension.

A former member of the provincial assembly and a leader of the Jamaat-e-Islami, Aslam Mujahid was abducted and shot dead by unknown persons on Monday evening.

He was tipped to be the religious parties' candidate for Karachi mayor in local elections due in a few weeks.

His funeral procession is expected to be attended by senior leaders of the Muttahida Majlis-e-Amal (MMA), the six party religious alliance, including alliance chief Qazi Hussain Ahmed.