LONDON - British human rights lawyers have raised their voice against the US drone strikes in Pakistan calling for the CIAs former legal chief to be arrested and charged with murder for approving attacks that killed hundreds of people. Amid growing international concern over the use of drones, lawyers and relatives of some of those killed are seeking an international arrest warrant for John A Rizzo, until recently acting general counsel for the CIA. Opponents of drones say the unmanned aircraft are responsible for the deaths of up to 2,500 Pakistanis in 260 attacks since 2004. US officials say the vast majority of those killed are 'militants. Earlier this week 48 people were killed in two strikes on tribal regions of Pakistan. The American definition of 'militant has been disputed by relatives and campaigners. The bid to arrest Rizzo is being led by British human rights lawyer Clive Stafford Smith of the campaign group Reprieve, and lawyers in Pakistan. They are also building cases against drone operators interviewed or photographed during organised press facilities. A first information report, the first step in seeking a prosecution of Rizzo in Pakistan, will be formally lodged early next week at a police station in Islamabad on behalf of relatives of two people killed in drone strikes in 2009. The report will also allege Rizzo should be charged with conspiracy to murder a large number of Pakistani citizens. Now retired, Rizzo, 63, is being pursued after admitting in an interview with Newsweek that since 2004 he had approved monthly drone attacks on targets in Pakistan, even though the US is not at war with the country. Rizzo, who was by his own admission up to my eyeballs in approving CIA use of enhanced interrogation techniques, said in the interview that the CIA operated a hit list. He also asked: How many law professors have signed off on a death warrant? Rizzo has also admitted being present while civilian operators conducted drone strikes from their terminals at the CIA headquarters in Virginia. Although US government lawyers have tried to argue that drone strikes are conducted on a solid legal basis, some believe the civilians who operate the drones could be classified as unlawful combatants.