The al-Qaida chief was living in a house in the town of Abbottabad that a U.S. official said was "custom built to hide someone of significance." Abbottabad is around 60 miles from the capital Islamabad, far from the remote mountain caves along the Pakistan-Afghanistan tribal border where most intelligence assessments had put bin Laden in recent years.
The house was close to the gate of the Kakul Military Academy, an army run institution where top officers train.
An American administration official said the compound was built in 2005 at the end of a narrow dirt road with "extraordinary" security measures. He said it had 12 to 18-feet walls topped with barbed wire with two security gates and no telephone or Internet service connected to it.
A Pakistan intelligence official said the property where bin Laden was staying was 3,000 square feet.
Critics have long accused elements of Pakistan's security establishment of protecting bin Laden, though Islamabad has always denied this. Ties between the United States and Pakistan have hit a low point in recent months over the future of Afghanistan, and any hint of possible Pakistani collusion with bin Laden could hit them hard even amid the jubilation of getting American's No. 1 enemy.
One Pakistani official said the choppers took off from a Pakistani air base, suggesting some cooperation in the raid. But President Barack Obama did not thank Pakistan in his statement on bin Laden's death.
Pakistan's foreign office hailed the death as a breakthrough in the international campaign against militancy, and noted al-Qaida "had declared war on Pakistan" and killed thousands of Pakistani civilians and security officers.
It stressed that the operation to kill bin Laden was an American one, and did not mention any concerns that Pakistani officials may have been protecting bin Laden in some way. Domestically, the government may yet face criticism by political opponents and Islamists for allowing U.S. forces to kill bin Laden on its soil.
Pakistani officials said a son of bin Laden and three other people were killed. Other unidentified males were taken by helicopter away from the scene, while four children and two woman were arrested and left in an ambulance, the official said.
A witness and a Pakistani official said bin Laden's guards opened fire from the roof of the compound in the small northwestern town of Abbottabad, and one of the choppers crashed. However U.S. officials said no Americans were hurt in the operation. The sound of at least two explosions rocked Abbottabad as the fighting raged.
It was not known how long bin Laden had been in Abbottabad, which is less than half a days drive from the border region with Afghanistan.
Salman Riaz, a film actor, said that five months ago he and a crew tried to do some filming next to the house, but were told to stop by two men who came out.
"They told me that this is haram (forbidden in Islam)," he said.
Abbottabad resident Mohammad Haroon Rasheed said the raid happened about 1:15 a.m. local time.
"I heard a thundering sound, followed by heavy firing. Then firing suddenly stopped. Then more thundering, then a big blast," he said. "In the morning when we went out to see what happened, some helicopter wreckage was lying in an open field."
"Intelligence analysts concluded that this compound was custom built to hide someone of significance," he said.
A Pakistani official in the town said fighters on the roof opened fire on the choppers as they came close to the building with rocket propelled grenades. Another official said four helicopters took off from the Ghazi air base in northwest Pakistan.
Last summer, the U.S. army was based in Ghazi to help out in the aftermath of the floods.
The officials spoke on condition of anonymity because of the sensitivity of the information.
Pakistan has in the past cooperated with the CIA in arresting al-Qaida suspects on its soil, but relations between its main intelligence agency and the CIA had been very strained in recent months amid tensions over the future of Afghanistan.
In late January, a senior Indonesian al-Qaida operative, Umar Patek, was arrested at another location in Abbottabad.
News of his arrest only broke in late March. A Pakistani intelligence official said its officers were led to the house where Patek was staying after they arrested an al-Qaida facilitator, Tahir Shahzad, who worked at the post office there.