The security alert at Magilligan Prison has now ended, the PSNI has confirmed.
All domestic and legal visits to the County Londonderry jail had been cancelled, a police spokesperson said.
The Point Road leading to the prison, the military of defence training site and the Foyle Ferry had also been closed due to the ongoing security situation.
A spokesperson for the PSNI said: “The security alert on the Point Road in Magiligan has now ended. ATO examined a suspicious object and have declared it to be nothing untoward.”