Pakistani security officials believe a relation of Osama bin Laden disappeared during the raid by a crack team of U.S. Navy Seals that killed the al-Qaida leader, deepening the confusion over the fate of a son regarded as the Crown Prince of Terror.

Three of bin Laden's widows, currently in Pakistani custody, have told interrogators that one son has not been seen since the operation on May 2.

The fresh details raise fears that the al-Qaida leader's youngest son and closest confidant, Hamza, may have escaped capture. The White House initially claimed that Hamza, 20, had been killed at the house in Abbottabad, about 30 miles from Islamabad, the Pakistani capital. Officials later said his 22 year-old brother Khalid had been killed instead. On Tuesday night an intelligence source in Islamabad told The Daily Telegraph that shifting accounts of what had happened, coupled with the widows' testimony, left them unable to account for one person they believe had been living in the house.

"We don't know if it was his son. Someone, one person, may have been in the compound that we now cannot account for if - we believe what we are being told," he said.

Bin Laden, who was married five times, had as many as 24 children.

No one knows for certain who was in the compound where he had lived, hidden in plain sight, for five years.

Hamza's mother Khairiah Sabar has been widely reported to be among the family members in Pakistani custody.

Thought to be the youngest of the Saudi-born terrorist's sons, Hamza has been described as the Crown Prince of Terror by Patrick Mercer, a Conservative MP.

He featured on an extremist website to mark the third anniversary of the July 7 London bombings in which 52 people died, reading a poem calling for "destruction" of America, Britain, France and Denmark.

Intelligence agencies believe he was being groomed as a possible future leader of al-Qaida. He was implicated in the assassination of Benazir Bhutto, the former Pakistani prime minister, in 2007.

More than a week after the wives and 12 children were picked up at the compound in Abbottabad, CIA interrogators have still not been given the chance to question them for crucial evidence.

U.S. officials said they believed they would soon be allowed access to the women, but a Pakistani government official denied that permission had been granted, saying local investigators had yet to finish their inquiry. "It's too early to even think about it," said the official.

Amid continuing tensions between Islamabad and Washington over the raid, U.S. officials have blamed the ISI, the Pakistani secret service, for leaking the name of the CIA station chief in Islamabad in retaliation. But they said that the agency veteran, who spends most of his time in the U.S. embassy compound, would not be withdrawn from the country.

It also emerged that the U.S. Navy Seals who killed bin Laden had permission to fight their way out of trouble and kill Pakistani forces if they were challenged during the operation.

It was decided that the team should be large enough to resist any Pakistani forces that reacted to the night operation, after President Barack Obama reportedly raised the prospect of a clash. As a result, two extra helicopters were deployed to protect the assault team.

"Their instructions were to avoid any confrontation if at all possible. But if they had to return fire to get out, they were authorized to do it," a senior U.S. administration official told the New York Times.

"Given our difficult relationship with Pakistan right now, the president did not want to leave anything to chance."