LONDON: A human rights group and a law firm took legal action Monday against the British government, accusing it of passing on intelligence to assist US covert drone attacks in Pakistan.

The London-based charity Reprieve and the law firm Leigh Day & Co. are filing papers to the High Court claiming that civilian staff at Britain's electronic listening agency, GCHQ, could be liable as ''secondary parties to murder'' for providing ''locational intelligence'' to the CIA in directing its drone attack program.

The two are acting on behalf of Noor Khan, 27, a Pakistani whose father was killed by a drone strike in northwest Pakistan in March 2011 while attending a gathering of elders. More than 40 other people were killed in that attack, they said.

Reprieve, which helps death row prisoners and Guantanamo Bay inmates, urged the British government to be more transparent about its role —if any —in the drone program.

''What has the government got to hide? If they're not supplying information as part of the CIA's illegal drone war, why not tell us?'' Reprieve director Clive Stafford Smith said.

British officials have never commented publicly on the drones. The Foreign Office and GCHQ declined comment on the legal action Monday, saying they could not speak about ongoing legal proceedings or and intelligence matters.

Since 2004, CIA drones have targeted suspected militants with missile strikes in the Pakistani tribal regions, killing hundreds of people.

The program is controversial because of questions about its legality, the number of civilians it has killed, and its impact on Pakistan's sovereignty.

Leigh Day & Co. did not detail what evidence the firm has regarding Britain's alleged role in the drone program, but it cited media reports that quoted an anonymous GCHQ source as saying that the assistance it gave to the US authorities was in 'strict accordance' with the law.

The law firm disputed that, saying GCHQ staff may be guilty of war crimes by passing along detailed intelligence to a drone program that violates international humanitarian law.