U.S. drone strikes on Pakistan and Yemen are in the spotlight again as two prominent human rights groups release reports on civilian deaths.

Amnesty International and Human Rights Watch are urging the Obama administration to end its secrecy over the attacks.

Amnesty International's report concentrated on two strikes in Pakistan last year which killed a grandmother and 18 civilian labourers.

The group says 68-year-old Mamana Bibi was blown apart in front of her family as she gathered vegetables.

But it says the U.S. government has stayed silent.

(SOUNDBITE)(English) AMNESTY INTERNATIONAL RESEARCHER MUSTAFA QADRI SAYING:

"Almost a year to the day her family has yet to receive any acknowledgement from the U.S. that she was killed by one of its drones, yet alone any justice or compensation for her killing."

Pakistan's prime minister, used a speech in Washington on Tuesday to condemn the strikes.

(SOUNDBITE)(English) PAKISTANI PRIME MINISTER NAWAZ SHARIF SAYING:

"Our political parties, in a national conference, declared that the use of drones is not only a violation of our territorial integrity but also detrimental to our resolve and efforts to eliminate terrorism from our country."

Human Rights Watch has launched a report on what it said were six unacknowledged attacks by the U.S in Yemen, at least four of them involving drones.

But its researchers say there've been many more and the death toll runs into hundreds.

(SOUNDBITE)(English) HUMAN RIGHTS WATCH RESEARCHER LETTA TAYLER SAYING:

"These strikes have killed an estimated 473 people yet the U.S. has only publicly acknowledged two fo these strikes - those that have killed Americans. It's as if the hundreds of Yemenis killed in these attacks simply never existed."

Both rights groups are urging the U.S to come clean about drone strikes and to investigate what they say may amount to unlawful killings.