Ministers could authorise more surgical airstrikes against Islamic State (IS) fighters in Syria amid claims that a "kill list" has been drawn up.
The roll of individuals who pose a direct threat to British citizens is said to be topped by the notorious "Jihadi John", who features in films of hostages being murdered.
Defence Secretary Michael Fallon insisted the Government would "not hesitate" to act again despite a backlash over the drone operation which killed militants Reyaad Khan and Ruhul Amin in the Islamic State stronghold of Raqqah on August 21.
The decision to authorise the use of remote RAF aircraft to strike individuals in Syria plotting attacks on the UK was taken "some months ago", according to Downing Street.
A meeting of senior members of the National Security Council, chaired by David Cameron earlier this year, received advice from the Attorney General that such attacks would be legal on grounds of self-defence.
The Prime Minister's spokeswoman declined to confirm or deny whether the meeting had drawn up a "kill list" of individuals for targeting, saying merely that the Government was "committed to doing what is necessary to protect British people here on the streets of Britain".
Mr Fallon told BBC Radio 4's Today programme: "There are other terrorists involved in other plots that may come to fruition over the next few weeks and months and we wouldn't hesitate to take similar action again."
He refused to be drawn on the number of terrorists planning attacks against Britain but said it was more than three, and revealed plots were also uncovered against Australia and the United States.
The Defence Secretary said the Government wanted to take wider military action against IS, also known as Isil or Isis, but a fresh vote would need to be held in the Commons, which rejected plans for airstrikes in Syria in 2013.
Labour leadership candidate Andy Burnham called for "greater accountability" from ministers on the drone strike.
"They must release the Attorney General's legal advice and any intelligence that can reasonably be put into the public domain to justify the imminence of the threat to the country," he said.
Former attorney general Dominic Grieve said targeted strikes would not be legal if they were used against an individual solely as "retribution" for past actions.
He told the foreign affairs select committee: "The fact that there might be a terrorist sitting in Raqqa who has done misdeeds in the past but is currently not doing anything, deciding you are going to kill him as a piece of retribution is not lawful in international law.
"It is not lawful in domestic law either, and bear in mind that domestic law applies to the actions of the UK Government, certainly in killing UK citizens anywhere in the world.
"So in those circumstances the justification has to be self defence: that you are stopping something happening and that you have good grounds for concluding that something is going to happen."
Members of the Muslim community in Khan's home town of Cardiff demanded to see the evidence that 21-year-old - who was the primary target of the drone strike - posed a threat to lives in Britain.
Former local councillor and family friend Mohammad Islam said: "Everyone is stunned that the Prime Minister has ordered the killing of a British national without getting parliamentary approval.
"The legality of this is not something that rests easy with people - especially given the past assurances about there supposedly being weapons of mass destruction in Iraq. I think it's only fair that people will be sceptical."
But the former UK ambassador to Afghanistan and Iraq, Sir William Patey, said he believed the public would have a "commonsense approach" to targeted strikes.
He told the BBC's Newsnight: "We're dancing on the head of a legal pin here. If the Government has information that they are plotting to attack us, why wouldn't they take them out?"