The RAF has been secretly targeting British jihadis plotting terror attacks against the UK from bases in Syria and Iraq, it is reported.
Drones and warplanes have been working their way through a "kill list" of key targets, according to the Daily Mail.
Neither Parliament nor the public has been told of the operation, the paper said.
The Ministry of Defence (MoD) did not comment directly on the report, but said anyone fighting for the Islamic State (IS) terror group in Iraq or Syria was a legitimate target "regardless of nationality".
However the Mail quoted a senior defence source as saying that the "priority" was those planning attacks on Britain.
"When we know where they are we kill them," the source is quoted as saying.
"Our priority is those plotting against the UK. We have found evidence of this.
"We are also helping the French who don't have our capabilities."
The MoD said British forces involved in the international coalition against IS, also referred to as Daesh, had "robust" target clearance processes and operated under strict rules of engagement in full compliance with international law.
"We and our coalition partners have been clear that if you are fighting for Daesh in Iraq and Syria then you will be targeted, irrespective of nationality," a spokesman said.
"The UK is committed to the defeat of Daesh and publishes regular updates on air strikes conducted by the RAF."
David Cameron sparked an outcry in September 2015 by authorising a drone strike which killed two British jihadis in Syria.
The attack took place before Parliament had voted to extend RAF operations against IS in Iraq into Syria.
In the Commons, the then prime minister justified the attack, saying that one of the jihadis, Reyaad Khan, 21, from Cardiff, represented a "clear and present danger" to the UK.
However the parliamentary Intelligence and Security Committee, headed by former attorney general Dominic Grieve, is reported to have questioned whether Khan represented a sufficient threat to justify the attack.