David Cameron has promised to ask "searching questions" of Pakistan after Osama Bin Laden was found living near the country's leading military academy.
But he said it was in the UK's national interest to recognise the countries shared a struggle against terrorism.
The president of Pakistan, Asif Ali Zardari, said the authorities there had not known where he was hiding when he was killed by US special forces.
US officials said Bin Laden must have had a "support system" in Pakistan.
Speaking in the Commons, the PM said the killing of Bin Laden was a "strike at the heart of international terrorism" and the UK would continue to co-operate with Pakistan and honour its aid promises because it was in "Britain's national interest".
He told MPs that "Pakistan has suffered more from terrorism than any other country in the world" and "Osama bin Laden was an enemy of Pakistan".
But he said the al-Qaeda leader's ability to live in a large house in Pakistan showed he had an "extensive support network" in the country and it was right to ask "searching questions" about that.
"We don't know the extent of that network so it is right that we ask searching questions about it and we will," he said.
Pakistan's main intelligence agency, the ISI, said it was embarrassed by "failures" which meant it was unaware that Bin Laden was hiding there.
UK embassies have been ordered to review security amid fears of reprisal attacks, and Britons have been urged to be vigilant.
Mr Cameron sparked a diplomatic row with Pakistan last year after accusing it of looking "both ways" on terrorism.
Earlier, he told the BBC's Today programme it would be wrong to "walk away" from Pakistan and have a "nuclear power in danger of massive extremism".
He also said Bin Laden's death would provide the opportunity to send a message to the Taliban to break their links with al-Qaeda, and take part in a "peaceful political process".
Labour leader Ed Miliband said the world was a "safer place" without Bin Laden and praised the "co-operative and calm response of the Pakistani government".
But he said there was a "great deal of uncertainty" about who was aware of the al-Qaeda presence in the country.
Meanwhile, Foreign Secretary William Hague has criticised Palestinian group Hamas for mourning Bin Laden's death.
Television channel al-Jazeera was also condemned in Parliament after broadcasting messages vowing vengeance for his execution.
Earlier, Mr Cameron was also asked by BBC Radio Five Live about reports that the information which led the CIA to Bin Laden may have come from a suspect at Guantanamo Bay under torture.
"We don't yet know that. The moral question in my view is that torture isn't justified," he said.
The Cabinet met at Downing Street on Tuesday morning and was followed by a gathering of the National Security Council, chaired by Mr Cameron.
Mr Cameron also spoke on Monday to the Pakistan and Afghanistan presidents.
Downing Street said the prime minister had made clear "Britain would continue to work extremely closely with both Afghanistan and Pakistan to tackle the terrorist threat from al-Qaeda and from the Taliban".
Bin Laden, believed to be behind the 9/11 attacks, was killed on Sunday about 62 miles from Pakistan's capital in an US operation which did not involve Pakistan.
Cabinet minister Baroness Warsi told the BBC that "none of us can say with absolute clarity" that no-one in the "formal or informal" sphere of the Pakistani authorities knew anything about Bin Laden's whereabouts but she was sure the "democratically-elected parts of the Pakistan government" had not known about his location.
The Foreign Office has urged Britons overseas to "exercise caution in all public places".
British military bases have been ordered to maintain a "high level of vigilance".
Meanwhile, the Prince of Wales is beginning a three-day trip to Washington, where he will meet US President Barack Obama at the White House.
The threat level to the UK from international terrorism has remained at severe since January 2010, indicating a terrorist attack is highly likely.
The Joint Terrorism Analysis Centre, which includes representatives from 16 government departments and agencies, sets the threat level.
Bin Laden was top of the US "most wanted" list, but managed to evade the forces of the US and its allies for almost a decade - despite a $25m (£15m) bounty on his head.
In the attacks in New York and Washington on 11 September, 2001, 67 Britons were among the 3,000 people killed when four planes were hijacked and flown into New York's World Trade Center, the Pentagon and a field in Pennsylvania.