Four men have been arrested by detectives investigating travel to Syria in support of alleged terrorist activity.
A 33-year-old man was arrested at Gatwick airport at 4.17pm on Wednesday as he attempted to take a flight out of UK, said a statement from the Metropolitan Police (MPS).
Between 6am and 6.30am on Thursday, three other men - an 18-year-old, a 31-year-old and a 22-year-old - were arrested at separate addresses in east London.
A spokesman said: "They are all in custody at a south London police station where they will be interviewed by officers from the MPS's counter-terrorism command."
Searches are continuing at three residential addresses in east London.
Jubayer Chowdhury, 24, was arrested by officers from the Metropolitan Police's Counter Terrorism Command at Heathrow Airport in November after arriving on a flight from Bahrain and is now facing charges in connection with the alleged plot.
Shajul Islam, 26, a trainee NHS doctor, who studied at St Bartholomew's and a University of London Hospital, is also accused of being part of an extremist group which held John Cantlie, who worked for various newspapers including The Sunday Times, and Jeroen Oerlemans for around a week in the war-torn state.
Islam, from Stratford, east London, was arrested at Heathrow Airport in October as he arrived back in the UK with his wife and one-year-old daughter on a flight from Egypt.
He is accused of being a doctor for the jihadi group which kidnapped the journalists and held them at a camp in Syria.
Islam is in custody pending a trial later this year.