A man from Hove is among three people to have been arrested by detectives from the Metropolitan Police Counter Terrorism Command.
And a property, in Maytree Walk, Hangleton, was searched by detectives on Friday evening (30 June).
After the arrests the force said: “Detectives from the Met Police Counter Terrorism Command, assisted by officers from Sussex Police, arrested two men in Essex and a third in East Sussex on Friday 30 June on suspicion of the commission, preparation or instigation of acts of terrorism.
“The men – aged 28, 31 and 28 – were arrested at approximately 6pm and are being held in custody under the Terrorism Act in a south London police station.
“Detectives have also executed search warrants at one address in East Sussex and three addresses in east London.
“Inquiries are ongoing.”