British police have detained four people on suspicion of planning terrorist attacks, the Associated Press reported.

The arrests were carried out in the morning by a counter-terrorism unit. The suspects were detained in their homes in Sheffield and Chesterfield, northern England. The police said it was questioning men and searching for four dwellings. The arrested are between the ages of 22 and 41. Against them there are no charges. Law enforcement have called on local residents to "remain vigilant, but not to worry."

There is a "serious" degree of terrorist threat in the UK, which means that there is a high probability of an attack.