Amnesty International investigated nine U.S. drone attacks in Pakistan and found evidence that more than 30 civilians were killed in four of the strikes.

A recent UN report estimates 400 civlians were killed by drone strikes in Pakistan over the last decade.

Most drone strikes occur in remote areas - making independent assessments difficult. And the U.S. government rarely acknowledges its role in individual strikes.

Amnesty International’s Naureen Shah is calling for official, public investigations into past drone strikes.

“We are asking President Obama to come clean about who the U.S. government is killing, not just to make a pledge of transparency or to make a promise that things are going right, but to say who has been killed, how many people have been killed and what the legal and factual justification for these killings was," said Shah.

The groups are also calling for more congressional oversight of the CIA and Defense Department, and reparations for innocent victims of U.S. drone strikes.