Precautionary security checks by the PSNI and An Garda Síochána have been carried out on trains travelling between Belfast and Dublin.
It follows information suggesting that a device of some description may have been left on one of the trains on Wednesday afternoon.
Nothing untoward has been found.
Police apologise for any inconvenience this may cause to passengers.
They ask anyone who sees anything suspicious to contact them on 101. A report can also be submitted online using the non-emergency reporting form via http://www.psni.police.uk/makeareport/ or through Crimestoppers anonymously on 0800 555 111 or online at http://crimestoppers-uk.org/.