The assailants wore white shirts and trousers, and sprayed gunfire in the air and at the police. One tossed a grenade in the direction of officers who had begun firing back.
Then, on a bustling workday morning in the heart of Pakistan's second-largest city, the explosives-laden van rammed the steel gate and detonated. The blast razed the police building, sheared off a wall from the intelligence agency office and destroyed any illusions that the military's incursion to retake parts of the country under Taliban control would succeed without great cost.
This morning, authorities put the death toll at 27, with more than 250 people injured. It was one of the deadliest terrorist attacks to strike Pakistan this year.
A group calling itself Tehrik-i-Taliban Punjab claimed responsibility, authorities said today. Some experts said they believed the attack could have been a retaliatory strike resulting from the Pakistani military's offensive against the Taliban to regain control of the embattled Swat Valley and surrounding districts that has sent hundreds of thousands of civilians fleeing from the fighting.
The bombers' target was clear. The van, laden with what Lahore police official Suhail Sukhera said was 220 pounds of explosives, detonated just outside buildings that housed the headquarters for the Punjab provincial branch of the Inter-Services Intelligence, Pakistan's spy agency; police offices; and the homes of several top local police officials.
"These buildings were sensitive," Sukhera said as he visited injured police officers at Sir Ganga Ram Hospital. Some officers had suffered gunshot wounds; others had large head and chest gashes created by the blast.
"What are we going to do? We're in a state of war," Sukhera said. "They're trying to harass us, but I'll tell you what: They'll fail. You'll see us back at our offices tomorrow."
Authorities said they had suspects in custody, but there were varying reports of how many were arrested. Sukhera said two men were detained. Pakistani television reported that as many as five people were being held. Pakistan's Dawn news channel reported that two of the suspects were connected to a group linked to Pakistani Taliban leader Baitullah Mahsud. The report, however, could not be verified.
Mahsud claimed responsibility for a daring daytime raid March 30 on a police academy on Lahore's outskirts that left about 20 people dead, including at least four assailants. In early March, militants attacked the Sri Lankan national cricket team during its visit to Lahore, leaving seven people dead, six of them police officers.
Since the offensive to oust the Taliban began a month ago, Pakistani military leaders have been touting the gains that troops have made against militants they have described as "on the run." Military spokesmen have said that more than 1,100 militants have been killed in the fighting.
On Wednesday, military officials said 70% of Mingora, Swat's main city, had been cleared of Taliban. Those claims could not be independently verified because the government has greatly restricted journalists' access to the Swat district.
The offensive has received growing public support, in part because many Pakistanis see the burgeoning Taliban insurgency as a significant threat to their country's stability and security. Terrorist attacks such as Wednesday's bomb blast in Lahore could be aimed at derailing popular backing for the offensive, analysts said.
"They're trying to get publicity, sending a message to 'Stop it!' trying to demoralize the public and hoping to get publicity for themselves through massive casualties," said Talat Masood, a military analyst and former general in the Pakistani army. "People then start criticizing the government for not negotiating. I hope it won't work."
Former Pakistani Interior Minister Aftab Khan Sherpao said that, given the toll that the offensive was taking on Taliban strongholds in Swat, Pakistani security forces should have been better braced for an act of retaliation.
"Such attacks are natural, and one should have expected them," Sherpao said. "Of course there was a security lapse -- that's why so many people died."
The van exploded after crashing through a security gate at a checkpoint just outside Lahore's Rescue 15 building, which houses police emergency services.
Khawar Abbas, a 25-year-old Lahore police officer assigned to guard the building, was about six feet from the van when it pulled up to the gate. Two men with automatic rifles jumped out and began firing into the air, then at Abbas and other police officers at the gate, Abbas said from his bed at Sir Ganga Ram Hospital, where he was recovering from a gunshot wound to his left arm.
Several officers fired back but were shot. Fahim Salim, 23, was shot twice in his left leg after firing at the gunmen.