The United States Secret Service is investigating an intruder at the home of national security adviser Jake Sullivan.

The alleged incident occurred in late April, when an unknown man walked into Sullivan's home at approximately 3 a.m., despite a round-the-clock security detail. The agents were allegedly unaware that a man had breached security, unnamed sources told the Washington Post.

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Sullivan, who instructed the man to leave, was not harmed during the incident, according to Secret Service Chief of Communications Anthony Guglielmi.

“Secret Service is examining a security incident that took place at a protectee site," Guglielmi told the Washington Examiner. "While the protectee was unharmed, we are taking this matter seriously and have opened a comprehensive mission assurance investigation to review all facets of what occurred. Any deviation from our protective protocols is unacceptable, and if discovered, personnel will be held accountable."

He added: "Modifications to the protective posture have also been made to ensure additional security layers are in place as we conduct this comprehensive review.”

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The man appeared intoxicated and did not know exactly where he was, including not knowing that he was in the home of the national security adviser, a source familiar with the incident told the Washington Post.

It is not clear whether any charges have been brought against the intruder.