A terrorist alert exercise at Dalton Barracks, Abingdon, has annoyed residents who were woken in the early hours of Wednesday morning.

They were roused from their beds at 4.05am by the sound of a piercing siren, as soldiers, the police and emergency services took part in a simulated terrorist attack.

The army regards the barracks as a potential target following the September 11 attacks on the World Trade Center and the Pentagon.

Ten residents complained to the barracks about the siren, which sounded for 15 minutes.

They received an apology, but were told the noise was part of an essential training exercise.

Station security officer Major James McIntosh said: "I understand and sympathise with local people who were woken by the noise of the siren.

"But it was necessary to alert all our personnel on site. "We couldn't give advance notice of the siren or the exercise, because that would have defeated the whole object of the training exercise.

"Since the events in New York last September we have been in a high state of alert against the possibility of terrorist action, and that is why we have to be prepared."

The exercise lasted six hours.

A simulated explosive device was found concealed in the barracks and was dealt with. The police, fire and ambulance services worked closely with the army. Maj McIntosh said: "This was the biggest exercise of its type at Dalton barracks for two years and was very successful."

Troops have been returning to Abingdon in the past month after tours of duty in Afghanistan, the Balkans, the Falklands and Kenya.