Over 300 stricks carried out by the U.S. spy planes have killed up to 775 civilians, including 173 children, in Pakistan tribal regions since June 2004, a report has said.

The report says between 1,141 and 1,225 persons were also injured by the drone strikes, mostly in Waziristan tribal areas near the Afghan border, said a report released yesterday by the London-based Bureau of Investigative Journalism.

The report, quoted by the Dawn newspaper, has mentioned varying figures about the casualties in the attacks as it said that at least 2,318 people and a maximum of 2,912 people, the majority of them alleged militants, have been killed in these attacks.

"The US covert drone war in Pakistan reached a new milestone with the 300th attack on alleged militants in the country’s tribal areas," says the opening of the report, adding that the attack by the Central Investigation Agency (CIA) is the fourth in North and South Waziristan in 48 hours.

Of the 300 drone strikes since June 17, 2004, it says, 248 occurred during President Barack Obama's first three years, rising to a frequency of almost one strike every four days.

The operations have angered many Pakistanis as hundreds of civilians have been killed. The Pakistani government publicly protests the operations, but is believed to support them.

The latest raids came as US special envoy to Afghanistan and Pakistan Marc Grossman arrived in Pakistan to improve ties between Washington and Islamabad.

Drone attacks are widely unpopular in Pakistan due to the civilian casualties they have caused [EPA]

Report: US drone strikes kill 775 in Pakistan