Two British ISIS fighters killed in secret RAF drone strike on Syria.

Two British fighters with the Islamic State in Syria have been killed in an RAF drone strike, David Cameron told MPs today. The Prime Minister said the strike in Raqqa on August 21 was "entirely lawful" and was ordered to stop a direct threat to Britain's national security.

But he faced criticism from Labour's acting leader Harriet Harman, who has demanded an investigation into the killing.

Reyaad Khan, 21, and Ruhul Amin were two of three jihadis killed for plotting attacks on British soil - despite the UK not having authority to strike in Syria.

Khan's family, who live in Cardiff, confirmed he had died last week.

A separate airstrike by US forces, also in Raqqa, killed British ISIS computer hacker Junaid Hussain on August 24.

Mr Cameron said the British strike on August 21 was the "only feasible means" of dealing with the terrorists and that it had been "necessary and proportionate".

The MP also said the threat to Britain from Islamist extremist violence is "more acute today than ever before" and in the last 12 months the police and security services had stopped at least six terrorist attacks against Britain.

“Both Junaid Hussain and Reyaad Khan were British nationals based in Syria who were involved in actively recruiting ISIL sympathisers,” he said.

They were involved in plots to attack ‘high-profile commemorations’ over the summer.

"We should be under no illusion," he said. "Their intention was the murder of British citizens.

"So on this occasion we ourselves took action. Today I can inform the House that in an act of self-defence and after meticulous planning Reyaad Khan was killed in a precision air strike carried out on 21 August by an RAF remotely piloted aircraft while he was travelling in a vehicle in the area of Raqqah in Syria."

The PM said two other ISIL fighters died with him, one of whom was British national Amin.

He added: "The action we took was entirely lawful. We were exercising the UK’s inherent right to self-defence.

"There was clear evidence of the individuals in question planning and directing armed attacks against the UK.