Lahore, March 13 (IANS) The toll in the twin suicide attacks here Friday has risen to 57, even as seven low-intensity blasts late at night kept police on their toes for over eight hours.

Nine security personnel were among those killed in the suicide bombings that wreaked havoc in the cantonment area, injuring 136 people.

According to police, two suicide bombers blew themselves up near security forces' vehicles in the RA Bazaar in the southern part of the cantonment, killing 57 people.

'The terrorists apparently changed their modus operandi in the...incident, as two suicide bombers carried out the blasts,' The News reported Saturday of the worst terrorist incident in the city.

'An interval of three minutes between the two attacks was a tactic devised by the terrorists to bring in more and more people to the site,' a security official said.

It was the second attack this week on security personnel in Lahore, which is considered the cultural hub of Pakistan. A car bombing hit a building housing the interrogation centre of a police intelligence agency Monday, killing 15 people and injuring around 70.

Forensic experts and officials of the bomb disposal squad believe the suicide bombers were wearing explosive-packed jackets weighing around 10 kg each, consisting of ball-bearings and shrapnel.

Inspector General Police Punjab Tariq Salim Dogar told reporters after inspecting the blast site: 'We have collected concrete technical evidence which will help identify the attackers. Both the attackers were on foot.' '

'The heads of both attackers have been found,' he added.

The impact of the blast was so severe that over a dozen vehicles were damaged while the windowpanes of nearby houses were shattered. A senior official of the bomb disposal squad said around 13 motorcycles, two motorcycle rickshaws, two bicycles and six private vehicles were badly damaged.

Five people were injured in the low-intensity explosions - six in Allama Iqbal Town police precincts and one in the Samanabad area of Lahore - late Friday.

The first explosive device went off in front of the Jamia Masjid Qadaria. Eyewitnesses said the device was buried in the ground.

The second explosion took place almost 150 yards away, with the bomb being planted in a car parked in front of the house of a military official, Inamul Haq.

The third explosion took place in a pickup near the Edhi Centre in Iqbal Town. The fourth device exploded in front of the house of Deputy Superintendent of Police Khalid Javed Chaudhry, damaging the main gate and smashing the windowpanes of the house.

The fifth explosion took place near a petrol pump in Karim Block and the sixth occurred near the Bismillah Chowk in Iqbal Town.

The seventh explosion took place in the Samanabad area. The bomb, placed in front of the house of Deputy Superintendent of Police Chaudhry Riaz Ahmad, exploded and broke windowpanes of several houses.