LONDON, Dec. 13 (Xinhua) -- Police counter terrorism units in London and central England arrested six people in early morning raids Monday.

The six, five men and a 32-year-old woman, are being held on suspicion of offences under Britain's terrorism laws and are being questioned at police offices.

Properties in London and in Derby and Burton-on-Trent are being searched as part of an ongoing investigation.

In Derby at least one street, Leopold Street, was cordoned off by police squads as enquiries continued.

So far police have not revealed whether the arrests have averted a planned terror attack in Britain. There has so far been no indication on the nationalities of the people being held in police custody.

In a brief statement, police said they have arrested four men from Derby -- aged 22, 27, 35 and 36 -- as well as a 27-year-old man from Burton on Trent and a 32-year-old woman from London.

The arrests all relate to suspicion of engaging in the Preparation of an Act of Terrorism, contrary to Section 5 of the Terrorism Act 2006.

The statement from the North East Counter Terrorism Unit added that six properties in Derby, Burton on Trent and London are all being searched as part of the investigation.

"Six people are currently in police custody. This is an ongoing investigation led by the North East Counter Terrorism Unit supported by local officers from Derbyshire, Staffordshire and the Metropolitan Police," added the statement.

Extra police were consigned to duties in the areas where the arrests took place to offer reassurance to local people and to speak to anyone who may have concerns.

"We would ask people to remain alert and vigilant but not to be alarmed and we are grateful for the assistance, support and understanding of people locally," the statement concluded.