London Met's counter-terror command said the arrests were 'pre-planned as part of an ongoing investigation'
British police have arrested four men in a series of raids on Wednesday in east London on suspicion of preparing terrorist attacks in the United Kingdom.
Special branch officers, the London Metropolitan Police's counter-terrorism unit, had detained the four men, aged 18, 24, 25 and 27, at their homes in east London.
"These arrests were pre-planned as part of an ongoing investigation by the Met's Counter Terrorism Command and (the domestic spy agency) MI5," police said in a statement.
"The arrests are linked to activity in the UK."
The men were being questioned at a south London police station "on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism", the statement added.
Britain has been on its second-highest alert level of "severe" since August 2014, meaning an attack by militants is considered highly likely.
In March, a man killed five people after driving into a crowd of pedestrians on Westminster Bridge in central London before stabbing a police officer in the grounds of parliament.
He was shot dead at the scene.
Earlier this month police charged three women from London with preparation of a terrorist act and conspiracy to murder after a raid in which one of the women was shot by armed officers.
In another incident last month, a man was arrested on Parliament Street, near the House of Westminster and UK Prime Minister Theresa May's Downing Street office, and later charged with terrorism and explosives offences.