Islamabad, Feb 2 : The United States will have to keep up an open-ended drone war against Al-Qaeda militants in Pakistan to prevent another terror attack on America, Defense Secretary Leon Panetta has said.

The assassination of Al-Qaeda figures in Pakistan, Yemen and Somalia with unmanned, robotic aircraft has provoked widespread criticism from human rights groups and some US allies, but Panetta stressed that the attacks had been effective.

Asked if the CIA "targeted killings" should be curtailed in coming years, said that there was still a need to continue the drone strikes more than a decade since the attacks of September 11, 2001, the Dawn reports.

According to the paper, the CIA drone bombing raids have caused an unknown number of civilian casualties and prompted accusations that the US is carrying out extra judicial killings in the shadows with no genuine oversight by courts or lawmakers.

Panetta said the campaign still needed to be regularly reviewed, but did not say he favored turning over the spy agency's drone war to the military, the report added. (ANI)