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The US Secret Service is investigating a break-in at the home of National Security Advisor Jake Sullivan.

Officials are looking into how an apparently intoxicated man was able to break into Mr Sullivan's home, evading security agents stationed outside, according to ´óÏó´«Ã½'s US partner CBS News.

The intrusion took place last month, a US law enforcement official said.

The man - who is still at large - reportedly walked into Mr Sullivan's home around 03:00 EDT (08:00 BST).

Mr Sullivan confronted the intruder - who did not appear to know Mr Sullivan or have an intention of harming him - and asked him to leave,

More than two Secret Service agents were parked outside and were not aware of the break-in until Mr Sullivan told them about it, a US law enforcement official told CBS.

The agency has launched an investigation into how this happened, the Secret Service said in a statement. "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," the agency added.

The law enforcement official told CBS that Mr Sullivan's Secret Service detail has been replaced and "additional security layers" added in the meanwhile.

The intrusion comes as elected officials and politicians face a rise in threats and harassment.

Earlier this week, a man attacked two staff members at a Democratic Virginia congressman's office with a baseball bat. A man also punched Minnesota Democratic lawmaker Angie Craig in a lift in her apartment building.

And last year, House Speaker Nancy Pelosi's husband Paul Pelosi was attacked with a hammer at his San Francisco home when his wife was not there.