Five men remain in custody after being detained near RAF Fairford in Gloucestershire, southwest England. British authorities are investigating possible preparation of a terrorist act and the circumstances surrounding reports of three suspicious vehicles heading toward the base.

Published accounts say police received a report at about 12:45 a.m. Sunday about three vehicles traveling toward RAF Fairford. Armed officers went to the Whelford area and detained five men. The men were first arrested under explosives-related law and later also held on suspicion of preparing a terrorist act. The investigation is in its early stages.

Authorities established a security cordon of about 400 meters around the vehicles. British Army specialists examined them, and roughly 85 homes were evacuated as a precaution. Residents who could not stay elsewhere were taken to a nearby leisure center. Police described the incident as major but said the situation was under control.

President Donald Trump said U.S. and British authorities had monitored the men for a long time and worked together on the arrests. He said the suspects intended to cause “major damage.” British authorities have not publicly provided evidence confirming a specific target or motive.

British Prime Minister Andy Burnham said the incident had caused deep concern in the local community and thanked police, counterterrorism officers and the armed forces. He urged the public to avoid speculation while inquiries continue.

RAF Fairford is an important facility used by the U.S. Air Force in Britain. Authorities have not announced evidence linking the five men to Iran or to a specific terrorist organization.