The United States is on the brink of being banned from using drones to strike militants in Pakistan, potentially ending one of the U.S. military's most effective campaigns against al Qaeda, the Associated Press reported Tuesday, citing various officials on both sides who spoke on condition of anonymity.

Although U.S. officials offered a series of key concessions -- including giving Pakistan's intelligence advance warning of any strike  -- the South Asian country flatly rejected all of them, adding to the strained relationship between Washington and Islamabad.

At a meeting in London in January, the director of the Central Intelligence Agency, David Petraeus, offered to give Pakistan's then-spy chief, Ahmed Shuja Pasha, advance notice of strikes and to apply new limits on targets that would end the CIA's practice of pre-emptive attacks on groups of armed men, the officials told the AP.