An armed group is holed up in a police academy in eastern Pakistan after attacking it with grenades and rifles. Officials say at least 11 people have been killed and dozens injured at the academy, on the outskirts of Lahore. Firing was continuing more than five hours after it began as troops laid siege to the academy. It is unclear how many people are trapped inside. The attack comes less than a month after gunmen attacked the Sri Lankan cricket team in Lahore. In that attack, six policemen were killed, while up to 14 gunmen escaped. Pakistani officials say it is too early to say who is responsible for Monday's assault in Lahore. Escalating militant violence in Pakistan has been concentrated in the country's north-west near the border with Afghanistan. But insurgents have increasingly targeted big cities in recent months. Compound surrounded The Lahore academy has been named by local media as the Manawan police training school. It is on the outskirts of the city, on a road to the border with India. One official said the gunmen had attacked from four sides. Another said they had thrown grenades before starting to fire. Several hundred trainees were there when they struck, local TV reports said. Some 10-12 gunmen carried out the attack, officials said. Troops were called in and secured the area around the academy. "Our elite squad has surrounded the area," said senior police official Mushtaq Sukhera. "God willing, now we will get into the building." The BBC's Jill McGivering, in Lahore, said that after hours of shooting, several hostages were seen coming out. She said helicopters were sweeping low over the compound, apparently trying to move the battle into a final, critical stage. Dressed as police The scene is chaotic, our correspondent says, with roads around the site clogged with vehicles and people. Officials and witnesses said the gunmen had entered the academy dressed in police uniform, adding to the confusion. A police constable who witnessed the attack told reporters: "We were exercising in the training ground inside the compound when we heard a blast. "A great cloud of dust blew over us and I felt something hit my face," he said. "When I touched my face there was blood all over. Then I saw a man firing a Kalashnikov running towards us. "He had a beard and his face was partially covered by a bandanna. Three of my colleagues fell down in the burst of firing. I just turned and ran." TV footage showed several police officers lying motionless on the ground inside the school. Reports gave varying death tolls. Police official Ali Nawaz told The Associated Press that at least 11 people had died, while 40-45 were being treated for injuries. Source:BBC