Five men have been arrested on suspicion of the commission, preparation or instigation of acts of terrorism, Scotland Yard has said.
The arrests were part of a "pre-planned, intelligence-led" operation by the Metropolitan Police counter-terrorism command.
The men, aged 21, 23, 24, 25 and 30, were all arrested at separate homes in Luton and have been taken to a central London police station for questioning.
Searches under the Terrorism Act 2000 are taking place at all five of the addresses and inquiries are ongoing, Scotland Yard said.
A spokesman said: "Officers from the counter-terrorism command have today, Tuesday April 24, arrested five men on suspicion of the commission, preparation or instigation of acts of terrorism.
"All five were arrested at separate residential addresses in Luton. They have been taken to a central London police station where they remain in custody.
"The arrests were a part of a pre-planned, intelligence-led operation. Search warrants were also executed under the Terrorism Act 2000 at five residential addresses in Luton in connection with this inquiry and searches are ongoing."