Police in Northern Ireland have launched an investigation into a security breach around the visit of the U.S. President Joe Biden.

A huge security operation was put in place for the visit ahead of Biden’s arrival on Tuesday evening for a four-day visit to the island of Ireland.

More than 300 officers from the rest of the UK had been drafted into Northern Ireland to support the Police Service of Northern Ireland (PSNI).

A document, which was marked PSNI and sensitive, was found by a member of the public, the BBC reported.

It was understood that it was an operational order which outlined officer deployments. However, no personal details on the President, his officials or those of other dignitaries associated with the visit were included within the document.

Responding, a PSNI spokesperson confirmed an investigation had been launched.

“We are aware of a security breach,” they said.

“An investigation has commenced, and we have notified the senior information risk officer.

“We take the safety of visiting dignitaries, members of the public and our officers and staff extremely seriously and will put the appropriate actions in place.”