Three men, aged 18, 22, and 31 were detained at separate addresses in east London between 6am and 6.30am today.
The arrests followed that of a 33-year-old man at Gatwick Airport yesterday at around 4.15pm, as he attempted to board a flight out of the country.
They are all in custody at a south London police station where they will be interviewed by officers from the Met’s Counter Terrorism Command.
Searches are ongoing at three properties in east London.
Two men have previously been charged in connection with this investigation.