Members of the unit, which was set up in 1996, have been transferred to broader operations that track Islamist groups.

The bin Laden unit, codenamed Alec Station, became less valuable as the movement's focus shifted more to regional networks of militants, said a US intelligence official who spoke on condition of anonymity on Tuesday.

"Al-Qaeda is no longer the hierarchical organisation that it was before 9/11. Three-quarters of its senior leaders have been killed or captured," the official said.

"What you have had since 9/11 is growth in the Islamic jihadist movement around the world among groups and individuals who may be associated with al-Qaeda, and may have financial and operation links with al-Qaeda, but have no command and control relationship with it," he added.

Hiding

Alec Station was established in 1996 after bin Laden's initial calls for global jihad, and employed about two dozen people.

The unit was strengthened after the September 11 attacks on New York and Washington that killed about 3,000 people.

The New York Times reported on Tuesday that the bin Laden unit was disbanded late last year and quoted its first director, Michael Scheuer, as predicting the move would harm the CIA's efforts to find bin Laden.
 
Bin Laden and his second-in-command, Ayman al-Zawahri, are believed to be hiding in the mountains along the Afghanistan-Pakistan border.