WORLD: Bomb kills 30 at Pakistan spy HQ

Several gunmen are said to have got out of the car and opened fire before detonating the device. There were reports of a gun battle raging.

Dozens of troops went into the damaged offices of the Inter-Services Intelligence agency to supervise the rescue work.

Shots were heard from inside the building an hour after the blast, which sent a huge cloud of white smoke into the air.

Twelve policemen and a child were among those killed. The explosion was so powerful it sheared the walls off buildings in the main business district. TV pictures showed emergency crews pulling injured people from the rubble. Heavy lifting gear was brought in and the death toll was expected to rise.

"Everything went dark in front of my eyes," said witness Muhammad Ali. "The way the blast happened, then gunfire, it looked as if there was a battle going on." Several suspects were reported to have been arrested. The attack was the third major strike in the city in recent months.

There are constant fears of retaliation from Taliban militants facing a major Pakistani military offensive in the Swat Valley, in the north-west. In March, gunmen attacked Sri Lanka's visiting cricket team in the heart of Lahore, killing six police officers and a driver and wounding several players.

Later that month, gunmen raided a police academy, leaving at least 12 dead during an eight-hour stand-off with troops. Pakistani Taliban chief Baitullah Mehsud claimed responsibility for that attack.

Militant violence has surged in nuclear-armed Pakistan in recent years, with numerous attacks on security forces and government and Western targets.

Lahore is capital of Punjab, Pakistan's most populous and prosperous province. The country's second biggest city is also traditionally home to top bureaucrats and senior military leaders.

Foreign Secretary David Miliband condemned the atrocity and said Britain was "committed to standing shoulder by shoulder with Pakistan in days of need". The Pakistani military is attacking the Taliban in the Swat Valley, a month-long operation the army says has already left 1,100 suspected militants dead.

The US needs Pakistani action against militants in the north-west to help defeat al Qaeda and disrupt the Taliban in Afghanistan. General David Petraeus, head of US Central Command, was in Islamabad today meeting military and political leaders.

Interior minister Rehman Malik blamed today's attack on militants from the Swat Valley and the Federally Administered Tribal Areas near Afghanistan. "These terrorists were defeated there and now they have come here," he said.

The offensive in Swat is seen as a test of the government's resolve to combat the spread of militancy, and is strongly backed by Washington and Pakistan's other Western allies.