Police have swooped on homes in Luton and arrested five men on terrorism charges.
The men - aged 21, 23, 24, 25 and 30 - were arrested on suspicion of commission, preparation or instigation of acts of terrorism.
The raids took place at 7am in the Bedfordshire town and involved scores of police.
"This morning's operation had not involved armed officers," a police spokesman said.
The arrests were part of a "pre-planned, intelligence-led" operation by the Metropolitan Police counter-terrorism command.
The five men have been taken to a central London police station for questioning.
A Bedfordshire Police spokeswoman said: "Full consideration has been given to treating those arrested, and especially their families, with appropriate respect for cultural and religious identity as far as is possible".
Searches are being carried out at the five houses and are expected to take at least a day.
The families of those arrested have been advised to find alternative accommodation.
"There is no danger to other nearby residents," the spokeswoman said.
The homes were in Bishopscote Road, Maidenhall Road, Crawley Green Road, Cornel Close and Shaftesbury Road.
In recent years, Luton has emerged as a flashpoint for tensions between Muslims and the far-right.