Three men have been arrested on suspicion of the commission, preparation or instigation of acts of terrorism.
Detectives from the Metropolitan Police's counter-terrorism command, assisted by officers from Sussex Police, arrested two men in Essex and a third in East Sussex at around 6pm on Friday.
The men, two aged 28 and one aged 31, are being held in custody at a south London police station.
Police have also executed search warrants at one address in East Sussex, and three addresses in east London.