Atlanta-based UPS said that the restrictions were the result of a government security check rather than a specific threat.

"Following careful consideration, the department has restricted the number of sites in the UK at which UPS Ltd are permitted to screen aircargo until it has satisfied current security requirements," the UK transport department said in a statement last week.

The department said that it could not give any details about the blocked sites for security reasons, the report said.

UPS spokeswoman Susan Rosenberg said that six of the company's British facilities - including its main air hub at East Midlands airport in central England - were still operating. She would not say how many facilities had been shut down.

UPS had told customers on Friday that shipments from Britain were being delayed. It said that 'areas of concern' were found during a government review of 'UPS procedures and employment documentation related to security'. It said that some facilities were temporarily taken offline, which has led to some delays in the movement of packages.

"UPS has activated contingency plans, communicated with customers and expects service levels to return to normal early next week," the company said in a statement. "UPS continues to work with all agencies around the world to maintain and enhance security and to balance necessary protections with the free flow of commerce, just as we have always done."