Terror struck Lahore [Images] for the second time in a month on Monday when heavily armed gunmen stormed a police academy near Lahore, killing at least 27 policemen in an eight-hour siege that ended with four terrorists being shot dead and six captured alive by security forces.

Clad in police uniforms, ten terrorists attacked the academy at 7 am and lobbed grenades and opened indiscriminate fire, killing guards at the gate. The audacious attack comes barely a month after the bus of the Sri Lankan cricket team was ambushed by terrorists on March 3, leaving eight people dead. Six cricketers sustained injuries in the attack.

The gunmen moved into a three-storied building in the police academy premises in Manawan, 12 kms from the Indian border, and held unspecified number of policemen as hostages. Elite commandos and security personnel surrounded the premises and used teargas shells to flush the terrorists out.

"The operation has ended with overpowering of a number of terrorists. While four were shot dead, several more were arrested," Interior Ministry chief Rehman Malik said. A joint investigation team has been formed to probe the attack, Malik said.

Security forces fired in the air and shouted 'Allah Ho Akbar' as the operation was successfully completed. Officials said the security personnel are clearing the area to assess the exact number of casualties. The dead included eleven police officers.

Television footage showed splattered blood and spent ammunition strewn on the roof of the building that was under siege. Soldiers and other security forces surrounded the compound on the outskirts of Lahore, exchanging fire in televised scenes reminiscent of last November's terrorist siege of Mumbai [Images].

Malik said the government suspected that terrorist outfits Lashker-e-Tayiba and Jaish-e Mohammad were behind the attack.

No group has claimed responsibility for the attack. Prior to the attack, a series of at least five blasts were heard at the training centre at Manawan.

Latif, a recruit who escaped from the centre with a dozen colleagues, said the policemen were busy training when the terrorists, many of them bearded, stormed the centre and threw grenades and opened fire.

Another recruit named Jehangir, who was injured, said he had seen about eight terrorists enter the centre and spray bullets at policemen.

"A number of my colleagues fell as they were hit by bullets. Then blasts occurred. Everyone was running for their lives and I was hit by a bullet in my left arm," he said.