ISLAMABAD: America's covert drone war on al Qaeda and the Taliban has killed up to 168 children in Pakistan over the last seven years, according to an independent study released Thursday.

The London-based Bureau of Investigative Journalism said its research showed there had been many more CIA attacks on alleged militant targets, leading to far more deaths than previously reported.

It said 291 CIA drone strikes had taken place in Pakistan since 2004, eight percent more than previously reported, and that under President Barack Obama there had been 236 strikes -- one every four days.

The Bureau said most of the 2,292 to 2,863 people reported to have died were low-ranking militants, but that only 126 fighters had been named.

It said it had credible reports of at least 385 civilians and a possible upper limit of 775 civilians being killed. It said there were reports of at least 164 children being killed and possibly up to 168.

Washington does not confirm Predator drone attacks, but US officials privately describe the program as vital in the fight against Islamist militants and say that the strikes are accurate, limiting any collateral damage.

“Civilian casualties do seem to have declined in the past year. Yet the Bureau still found credible evidence of at least 45 civilians killed in some 10 strikes in this time,” said the Bureau's report.

The most recently reported civilian fatality was a migrant worker on leave from Dubai who was killed on July 12 when the CIA attacked a car carrying eight alleged militants, according to the Bureau's researchers in Waziristan.

On Wednesday, Pakistani security officials said up to 21 Afghan fighters from the al Qaeda-linked Haqqani network, considered the top US foe in eastern Afghanistan, were killed in a drone strike in North Waziristan.

Pakistan's lawless tribal belt where the drone strikes are carried out is off limits to independent access by journalists and aid workers.