The number of civilians killed in CIA drone strikes in Pakistan and Yemen is greater than the United States has acknowledged, two human rights groups said in separate reports released today.

Amnesty International and Human Rights Watch also called for the United States to open investigations into attacks they say have killed or wounded civilians in those countries.

The independent reports documented specific cases in which the groups said civilians with no ties to al Qaeda terrorists were killed in U.S. drone strikes. The CIA uses lethal missile strikes targeting al Qaeda operatives in Pakistan's tribal areas and Yemen.

Amnesty International's report, titled "Will I be next? US drone strikes in Pakistan," looked at nine of the 45 drone strikes carried out in Pakistan's North Waziristan area from January 2012 to August of this year.

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One of those strikes last October killed Mamana Bibi, a 68-year-old grandmother, as she was working in the fields near her home. The report also details a missile strike in the village of Zowi Sidgi that targeted a tent that killed 18 miners, including a 14-year-old who had gathered for a meal there. A second missile strike targeted those who had gathered to help the injured from the first missile strike.

"We are extremely concerned that these and other killings documented in our report may constitute extrajudicial executions or war crimes," Mustafa Qadri, Amnesty International's Pakistan researcher, said at a news conference releasing the report.

Human Rights Watch's report, "Between a Drone and al-Qaeda': The Civilian Cost of US Targeted Killings in Yemen," examined six U.S. strikes in that country from 2009 to the present that it said killed 57 civilians. Two of the attacks involved cruise missiles launched from U.S. Navy ships.

The Human Rights Watch report concluded that in two of the six incidents, the United States had "indiscriminately killed civilians."

"This is a clear violation of international law, even if it was not the U.S. intent," report author Letta Tayler said. "If it indiscriminately killed, it should be held responsible."

It appeared that the U.S. attacks were disproportionately killing civilians, she added. One of the cruise missile attacks killed 14 suspected members of al Qaeda in the Arabian Peninsula, but also killed 41 civilians, including women and children. Another strike struck 12 civilians riding in a passenger van.

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White House press secretary Jay Carney today said the administration was "reviewing these reports carefully" but defended the U.S. course of action.

"To the extent these reports claim that the U.S. has acted contrary to international law, we would strongly disagree," he said. "The administration has repeatedly emphasized the extraordinary care that we take to make sure counterterrorism actions are in accordance with all applicable law."

He added: "We are choosing the course of action least likely to result in the loss of innocent life."

The number of drone strikes in Pakistan increased significantly under the Obama administration, peaking at 117 in 2010, according to statistics compiled by the Long War Journal blog. The number has decreased in the years since, with 23 having taken place so far this year, the lowest total in six years.

Statistics from the same blog indicate that the number of CIA and U.S. military drone strikes carried out in Yemen peaked last year at 42. There have been 22 strikes so far this year.

The authors of the critical reports acknowledged that they faced a wall of silence from the U.S. government in response to their requests for help in gathering information about the incidents detailed in their reports.

The "most challenging situation we had to face was the complete and utter secrecy of the U.S. government," Amnesty International's Qadri said.

Both organizations said they worked with local nongovernmental agencies in both countries to conduct multiple cross-referenced interviews with eyewitnesses. Amnesty International used satellite imagery to locate some of the attack sites in Pakistan's tribal regions.

Andrea Prasow, a senior counterterrorism counsel for Human Rights Watch, said her organization pointed out unlawful killings, but was not calling for an end to the U.S. drone program nor labeling them unlawful weapons. "We recognize that in some cases drones may be more protective of human life than other types of weapons, "she said.

Instead Prasow said both reports wanted the Obama administration to provide more transparency and accountability about its legal justification for CIA drone strikes and how the United States is in compliance with international legal norms.

Naureen Shah, an advocate with Amnesty International, blasted the administration, saying, "The U.S. is acting like a hit-and-run driver refusing to take responsibility for the killing of a 68-year-old woman and a 14-year-old boy."

In a May speech at the National Defense University, President Obama announced tighter restrictions that limited the use of drone strikes against those who posed imminent threats. He also said at the time that U.S. drone strikes are only conducted when there is "near-certainty that no civilians will be killed or injured."

The reports were released on the eve of Pakistan Prime Minister Nawaz Sharif's' meeting with Obama at the White House. Sharif has been vocal in his opposition to the CIA drone strikes in his country. The Amnesty International Report said it had found indications that Pakistani government institutions might be facilitating the drone strikes. Qadri said such activity could constitute human rights violations.

The United Nations General Assembly will discuss Friday two new reports on drone strikes and extrajudicial killings compiled by Ben Emerson, the U.N. Special Rapporteur on human rights and counterterrorism.

In the drone report, Emerson says Pakistan's Foreign Ministry has recorded at least 330 U.S. drone strikes in its tribal areas since 2004. Pakistan's government believes that at least 400 civilians have been killed by U.S. drone strokes.