Getty ImagesRoyal Mail says it is unable to send letters and parcels overseas after a “cyber incident”.
It is telling customers to stop sending items overseas while it tries to resolve the issue.
The firm said there were also minor delays to deliveries into the UK, but domestic deliveries are unaffected.
It apologised and said its teams were “working around the clock to resolve this disruption” and would update customers when it had more information.
Royal Mail is understood to be calling it a “cyber incident” rather than an attack because it does not know what has caused the issue.
A spokesperson said: “We immediately launched an investigation into the [cyber] incident and we are working with external experts.”
They said it had reported the incident to the relevant security authorities.
In the year to March, Royal Mail sent 152 million parcels abroad which equates to around 200,000 items a day.
However, that was a small fraction of the number of parcels it sent domestically.
