The UK government said its drones does not have a “targetted killing” policy. However, the Joint Committee on Human Rights said the UK was willing to use lethal force in the Middle East and overseas.
The drone case involves the killing of a UK citizen in Syria by an RAF drone.
Reyaad Khan, who joined the Islamic State in Syria, was killed by a military-operated drone August of 2015.
British Prime Minister David Cameron said the 21-year-old from Cardiff plotted to attempt “barbaric” attacks on UK soil.
He justified the attack was an act of self-defence in that regard.
“Although the government says that it does not have a ‘targeted killing’ policy, it is clear that it does have a policy to use lethal force abroad outside armed conflict for counter-terrorism purposes.
“Certain aspects of the government’s view of the legal basis for its policy require urgent clarification,” they said.
Committee chairman and Labour MP Harriet Harman said the legal justification for the drone strike on Khan had been “confused and confusing”.
She called for the UK government to lead the way internationally by defining a clear legal basis for action, and making sure those who made decisions were held accountable.
“As the world faces the grey area between terrorism and war, there needs to be a new international consensus on when it is acceptable for a state to take a life outside of armed conflict,” she said.
A government spokesman said: “We are clear that where we identify a direct and imminent threat to the UK we will take lawful action to address it and report to Parliament after we have done so.
“Such actions are only to be carried out as a last resort when all other options have been exhausted, and we would always do so in accordance with international humanitarian law.”