Detectives have been granted a warrant to hold the arrested six for a week
A counter-terrorism unit has been given more time to question six people arrested on suspicion of offences under the Terrorism Act.
Four men from Derby, a man from Burton upon Trent and a woman from London were arrested on Monday.
Six properties in Derby, Burton upon Trent and London were all searched as part of the operation.
Detectives from the North East Counter Terrorism Unit have been granted until 19 December to question the six.
The BBC understands the operation was regarded as "significant" and the result of an ongoing investigation.
Six properties in Derby, Burton upon Trent and London have been searched as part of the operation
Sources said the investigation was into a group believed to be working towards an attack - though a strike was not thought to be imminent.
An Army bomb disposal team was deployed to the Normanton area of the city as a precautionary measure.
The four suspects from Derby are aged 22, 27, 35 and 36. The suspect from Burton upon Trent is aged 27 and the woman from London is 32.
The investigation is being led by the North East Counter Terrorism Unit, supported by local officers from Derbyshire, Staffordshire and the Metropolitan Police.
Detectives have been given a further seven days from the time of the arrests on Monday.
- Published12 December 2016
