No group immediately claimed responsibility for the early morning strike in an army cantonment in Peshawar, the main city in Pakistan's volatile northwest. But it added to growing fears of a long, violent summer ahead as the Pakistani Taliban and other al-Qaida affiliated groups carry out threats to avenge the al-Qaida chief's slaying.
Already this month, the Pakistani Taliban have claimed they carried out three revenge attacks, including a deadly 18-hour siege of a naval base.
The bomber's target Wednesday appeared to be a building belonging to the police's criminal investigation department, although military facilities also are nearby, said Liaquat Ali Khan, a senior police official in Peshawar.Investigators with the counter-terrorism unit of the police were stationed at the center, said Fayaz Khan Toru, the top police official in northwestern Khyber-Pakhtunkhwa province.
Police officer Mohammad Zahid was in the basement of the building when the bomb went off.
"I felt like the sky fell on me," Zahid said in the hospital, where he was being treated for multiple injuries. "The explosion jammed the door of my room in the basement, but there was a small hole in the wall so I crawled through that. When I got outside, there was lots of dust and smoke."
At least five police officers died, and 30 people were wounded, police official Jalal Khan said. Military forces quickly sealed off much of the cantonment as machines were brought in to sift through the huge piles of rubble left at the site of what was once a multistory building.
"Our determination is much higher than before, and we will fight till the defeat of these terrorists," said Bashir Bilour, a senior official with the provincial government. He said at least 660 pounds (300 kilograms) of explosives were used.
Bin Laden was killed on May 2 by a team of U.S. Navy SEALs in the army town of Abbottabad, elsewhere in Pakistan's northwest and roughly a mile away from Pakistan's premier military academy.
Since the raid, U.S.-Pakistan relations have sunk to new lows. Pakistani leaders insist they had no idea the al-Qaida leader had been living, apparently for five years, in the large, three-story house in Abbottabad. And they are furious that the U.S. raided the house without telling them in advance.
The Pakistani Taliban are exploiting the tense relations by promising to attack both Western and Pakistani targets to avenge bin Laden's death. The militant group has long despised the Pakistani government and army for their alliance with the U.S., a sentiment shared by many ordinary Pakistanis.
Since the bin Laden raid, the group has taken responsibility for a twin suicide bombing at a paramilitary police training facility that killed around 90 people and a car bomb that slightly wounded two Americans in northwest Pakistan.
But the siege of the naval base in the southern port city of Karachi was easily one of the most audacious militant assaults in years and further rattled a military establishment already humiliated by the unilateral U.S. raid.
The militants destroyed two U.S.-supplied surveillance aircraft while killing 10 people on the base. Four militants died in the fighting, officials said.
There have been conflicting accounts as to the number of insurgents involved - anywhere from six to 15. Pakistan security agencies are known to sometimes not give full accounts of terrorism incidents and often hold suspects for months without informing the public.
The fact that the attackers managed to infiltrate so deep into the high-security base led to speculation they may have had inside information or assistance. The military is not immune from the anti-Americanism and Islamism coursing through the country, especially in its lower ranks, and America's raid against bin Laden has exacerbated anger among soldiers.
The naval base standoff also revived international concerns over whether Pakistan's estimated 100 nuclear weapons were safe from extremists. During a news conference Tuesday in Kabul, NATO Secretary General Anders Fogh Rasmussen acknowledged the ongoing concerns about the safety of Pakistan's nuclear weapons.
"Based on the information and intelligence we have, I feel confident that Pakistan's nuclear arsenal is safe and well protected," Rasmussen said. "But of course, it is a matter of concern and we follow the situation closely."