Britain's Royal Mail is experiencing "severe service disruption" to its international export services following a cyber incident, the company has announced.
A statement said it was temporarily unable to dispatch export items including letters and parcels to overseas destinations.
Royal Mail said: "We have asked customers temporarily to stop submitting any export items into the network while we work hard to resolve the issue.
"Some customers may experience delay or disruption to items already shipped for export.
"Our import operations continue to perform a full service with some minor delays.
"Our teams are working around the clock to resolve this disruption and we will update customers as soon as we have more information.
"We immediately launched an investigation into the incident and we are working with external experts.
"We have reported the incident to our regulators and the relevant security authorities.
"We would like to sincerely apologise to impacted customers for any disruption this incident may be causing."