Defence Secretary Michael Fallon said Britain "wouldn't hesitate" to strike again after the killing of 21-year-old Reyaad Khan in Syria, even as doubts were raised about the legality of the action.
"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," Fallon told BBC Radio 4's Today programme.
"It's extremely dangerous because these are attacks that have been and are being planned against major public events on our streets," he said.
Cameron came under pressure to give further details of attacks allegedly plotted by Khan, who left home to join IS in 2013, as the legality of the move was questioned by opposition MPs and rights campaigners.
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Cameron told parliament Monday the strike was "an act of self-defence" since Khan had been planning "barbaric" attacks in Britain against high-profile public events over the summer.
Ministers said the decision had been taken on advice from the attorney general, Britain's chief legal advisor.
"The advice here is absolutely clear -- that any country has the right to self defence, to protect itself from armed attack," Fallon said.