Pakistan interrogated on Tuesday four suspects, including an Afghan, captured during a police academy siege that has fanned Western fears about the menace of extremism in the nuclear-armed state.
Attackers armed with guns, grenades and suicide vests stormed the training centre near Pakistan's cultural capital Lahore unleashing nearly eight hours of gunbattles until they were overpowered by security forces.
Eight police cadets and four attackers died in the second commando-style assault in Lahore this month, sparking fears that violence is seeping out of the tribal badlands on the Afghan border and into the heart of Pakistan.
Such is the scale of unrest in the frontline state of the "war on terror" that US President Barack Obama called Al-Qaeda and its allies "a cancer that risks killing Pakistan" and urged Islamabad to eradicate extremists.
"Police and other intelligence agencies are interrogating the suspects. We cannot say anything for now about which group is involved," Lahore city police chief Habib-ur Rehman told AFP.
Authorities have spearheaded a top-level investigation, with homegrown Islamist groups or radicals holed up on the border with Afghanistan the chief suspects.
The Afghan border area is awash with Taliban and Al-Qaeda militants.
"In three days we will give you details of the investigation," interior ministry chief Rehman Malik told a news conference in Lahore.
Malik talked about possible "foreign hands" but did not name any country. The attack took place near the border with Pakistan's arch rival India.
"Terrorists are coming from FATA (the semi-autonomous Federally Administered Tribal Areas on Pakistan's border with Afghanistan). They get help from across the border," he said. "Where do they get weapons and new vehicles?"
A funeral ceremony was scheduled for the eight dead cadets at a police building in downtown Lahore on Tuesday. The bodies will then be taken to their home towns for burial, the city police commander told AFP.
British Foreign Secretary David Miliband condemned the attack and pledged international help to root out the extremist threat.
"The attack is yet another reminder of the threat that Pakistan faces from violent extremism," he said.
"It is a threat that the international community must help Pakistan to tackle, in the interests both of Pakistan's people and of wider stability."
Police instructor Mohammad Iqbal, lying in hospital with head and spinal injuries, speculated that the attack was to avenge a Pakistani security operation against radicals holed up in an Islamabad mosque in July 2007.
"What I vividly remember is that they kept hurling grenades and fired from the second floor of the building where they later got trapped, and every time they shouted Allahu akbar (God is greater)," he told AFP.
"My hunch is they took revenge on us for the Red Mosque operation," he said.
Basharat Ali, with a swollen, fractured leg and on a drip, said he was proud to be a policeman despite what he called "the worst day of my life".
"I saw many of my colleagues wounded. I also saw a policeman who died on the spot. There were three or four people who were throwing grenades and firing at policemen. They were running here and there like shadows," he said.
Non-governmental group the Centre for Peace and Development Initiatives said Monday's attack -- coming so soon after the attack in the same city on the Sri Lankan cricket team -- underscored the urgent need to strengthen the police.
"Had the perpetrators of the attack on the Sri Lankan team been arrested, this incident of violence might not have taken place," it said.
"The cancer of terrorism is fast spreading and remedial measures need to be taken on a war-footing," the centre added.
Pakistan, under US pressure to eliminate extremists, denied that there was another breakdown in security, four weeks after gunmen ambushed the Sri Lankan cricket team, killing eight people before calmly walking off unchallenged.
Pakistani officials said that attack bore the hallmarks of the November 2008 siege in India's financial capital Mumbai, blamed on Pakistani militants, which killed 165 people.
Analysts said the latest attack was a firm message to Obama, who has put Pakistan at the heart of the fight against Al-Qaeda, tripling US aid in a strategy aimed at reversing the war in neighbouring Afghanistan.