The UK is currently facing a "series of plots and terror attacks", the Defence Secretary has told ITV News.
Mr Fallon has warned that further attacks on UK soil are being planned by "a number" of so-called Islamic State militants inside Syria, but could not give out specific details because of security reasons.
Earlier, Fallon said the Government would "not hesitate" to repeat the action that led to Britons being killed by an RAF drone in the Islamic State stronghold of Raqqah last month, and that further strikes were possible.
Defence Secretary Michael Fallon has suggested there were more names on the list who were legitimate targets for air strikes.
The daughter of murdered aid worker David Haines tells ITV News drone strikes against Islamic State are "a step in the right direction".
Two British Islamic State fighters were killed by a RAF drone strike in Syria, while a third died during an American attack.