The UK would not hesitate to launch more secret drone strikes in Syria to thwart terror plots, Defence Secretary Michael Fallon has said.
He said the RAF strike that killed two British Islamic State jihadists was a "perfectly legal act of self defence".
There are "other terrorists" involved in "other plots that may come to fruition" in weeks or months, he said.
Meanwhile, the father of two more Britons thought to be in Syria said he believed they were now on a "hit list".
Ahmed Muthana, father of Nasser, 20, and Aseel Muthana, 17, from Cardiff, said he thought the pair could be killed in a similar drone strike because the UK government is "targeting everyone now".
Earlier, Mr Fallon would not be drawn on whether the UK had a "hit list".
'Barbaric attacks'
But he told the BBC: "There are a large number of individuals - not all British - out there in Syria... who are actively involved in planning armed attacks here in Britain."
BBC security correspondent Frank Gardner said if such a list existed, it "would be something drawn up digitally", and based on intercepting online communications, or human informants.
A debate over the UK's use of drones started after MPs were told on Monday that Cardiff-born Reyaad Khan, 21, had been killed in a precision strike in Raqqa by a remotely piloted aircraft.
Ruhul Amin, 26, from Aberdeen, was also killed in the attack on 21 August.
Video at link:
http://www.bbc.co.uk/news/uk-34181475
