British police arrested 10 men Wednesday in a series of anti-terrorist raids across northwest England.
Greater Manchester Police said the suspects were detained in raids across a wide area including the cities of Manchester and Liverpool.
The force said several addresses were being searched.
Police would not give any details of the alleged plot.
At least one of the raids was in the working-class Cheetham Hill area of Manchester, which has a large South Asian community.
Witnesses said another raid was at Liverpool's John Moores University. Footage recorded on a mobile phone showed armed police standing over a man lying on the floor of a university building.