WASHINGTON — The US Secret Service said Tuesday it is investigating how an intruder was able to break into the home of White House national security adviser Jake Sullivan in the middle of the night a few weeks ago.

An agency spokesman said they are investigating «a security incident that took place at a protected site.»

«While the protégé was uninjured, we are taking this matter seriously and have opened a comprehensive mission assurance investigation to review all facets of what occurred,» Secret Service spokesman Anthony Guglielmi said in a statement.

«Any deviation from our security protocols is unacceptable and if discovered, staff will be held accountable. Modifications have also been made to the security posture to ensure additional layers of security are in place while we conduct this comprehensive review,» he added.

White House National Security Adviser Jake Sullivan in Washington on January 13, 2022.File Andrew Harnik / AP

Guglielmi did not say what happened to the intruder. The White House declined to comment to NBC News.

The Washington Post, which first reported the intrusion, he quoted three government officials who said the incident occurred around 3 a.m.

Sullivan confronted the person and told him to leave, the Post reported, citing two of the people briefed on what happened.

Sullivan, 46, has served as Biden’s national security adviser since the start of his presidency, serving from 2013 to 2014 as Biden’s national security adviser when he was vice president. Sullivan held other positions in the Obama administration and also served as former Secretary of State Hillary Clinton’s top foreign policy adviser during her 2016 presidential campaign.

The break-in at Sullivan’s home comes as elected officials and other public figures have faced increased threats in recent years.

On Monday, a 49-year-old Virginia man with a metal baseball bat entered the D-Va. district office of Rep. Gerry Connolly and allegedly attacked two members of the congressman’s staff.

In October, a man attacked Paul Pelosi, the husband of then-Speaker of the House Nancy Pelosi, D-Calif., with a hammer at their home in San Francisco. The man who was charged in the attack reportedly said that he was looking for the Speaker of the House at the time. The defendant in the case has pleaded not guilty to state and federal charges.