The men, aged between 18 and 27, were suspected of involvement in the commission, preparation or instigation of acts of terrorism, the Metropolitan Police (Met) said.
"All four men have been detained under TACT (Terrorism Act) and are at present in custody at a south London police station. Officers are currently searching five residential addresses in east London and one business address, also in east London," the Met said in a statement.
"These arrests were pre-planned as part of an ongoing investigation by the Met's Counter Terrorism Command and MI5. The arrests are linked to activity in the UK," it said.
The arrests follow heightened security alert in London following an attack on Parliament by Khalid Masood in March that claimed four innocent victims and the arrest last month of Khalid MohamedOmarAli, who was arrested with knives near Downing Street.
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