US forces finally found Al Qaeda leader Osama bin Laden not in the rugged mountains of Afghanistan's border, but in a million-dollar compound in an upscale suburb of Pakistan's capital, with his youngest wife, US officials said early on Monday.

They were led to the fortress-like three-storey building after more than four years tracking one of bin Laden's most trusted couriers, whom US officials said was identified by men captured after the September 11, 2001 attacks.

'Detainees also identified this man as one of the few Al Qaeda couriers trusted by bin Laden. They indicated he might be living with or protected by bin Laden,' a senior administration official said in a briefing for reporters.

Bin Laden was finally found -- more than 9-1/2 years after the 2001 attacks on the United States -- after authorities discovered in August 2010 that the courier lived with his brother and their families in an unusual and extremely high-security building, officials said.

'When we saw the compound where the brothers lived, we were shocked by what we saw: an extraordinarily unique compound,' a senior administration official said.

'The bottom line of our collection and our analysis was that we had high confidence that the compound harbored a high-value terrorist target. The experts who worked this issue for years assessed that there was a strong probability that the terrorist who was hiding there was Osama bin Laden,' another administration official said.

The home is in Abbotabad, a town about 35 miles (60 km) north of Islamabad, that is relatively affluent and home to many retired members of Pakistan's military.   

The building, about eight times the size of other nearby houses, sat on a large plot of land that was relatively secluded when it was built in 2005. When it was constructed, it was on the outskirts of Abbotabad's center, at the end of a dirt road, but some other homes have been built nearby in the six years since it went up, officials said.

Intense security measures included 12- to 18-foot (3.6 meters to 5.5 meters) outer walls topped with barbed wire and internal walls that sectioned off different parts of the compound, officials said. Two security gates restricted access, and residents burned their trash, rather than leaving it for collection as did their neighbors, officials said.

Few windows of the three-storey home faced the outside of the compound, and a terrace had a seven-foot (2.1 meter) privacy wall, officials said.   

'It is also noteworthy that the property is valued at approximately $1 million but has no telephone or Internet service connected to it,' an administration official said. 'The brothers had no explainable source of wealth.'    

US analysts realized that a third family lived there in addition to the two brothers, and the age and makeup of the third family matched those of the relatives -- including his youngest wife -- they believed would be living with bin Laden.

'Everything we saw, the extremely elaborate operational security, the brothers' background and their behavior and the location of the compound itself was perfectly consistent with what our experts expected bin Laden's hide-out to look like,' another Obama administration official said.   

A small US team conducted a helicopter raid on the compound on Sunday afternoon, officials said. After 40 minutes of fighting, bin Laden and an adult son, one unidentified woman and two men -- identified as the courier and his brother -- were dead, officials said.

Abbotabad is a popular summer resort, located in a valley surrounded by green hills near Pakistani Kashmir. Islamist militants, particularly those fighting in Indian-controlled Kashmir, used to have training camps near the town. - Reuters