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, a statement from the Metropolitan Police (MPS) said.
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.