An intruder was able to gain access inside the security at Joint Base Andrews, where the U.S. president's planes are kept, and even made his way inside one of the jets used to transport the country's top government officials and first ladies.

An official of the Joint Base Andrews in Maryland confirmed the incident and that an investigation is underway. "An unauthorized individual gained access to Joint Base Andrews," The Independent quoted the spokesperson as saying.

Base officials did not answer questions about whether the person was taken into custody, how far he has made it into the military facility, or if he was able to access any of the presidential planes.

But according to the U.S. Air Force Office of Special Investigations, it has detained and interrogated the intruder on Thursday, after he sneaked past security and onto the base.

The U.S. 89th Airlift Wing is the unit in charge of flying the president on board the VC-25 plane, popularly referred to as "Air Force One," including the vice president, members of the Cabinet, and other high-ranking officials with its fleet of advanced aircraft.

"Everyone is taking this very seriously," U.S. Department of Defense spokesperson John Kirby said Friday. The intruder was unarmed, and no suggestion has been made that the trespasser is connected to any extremist organization, the official said.

"The security of our installation is paramount," Col. Roy Oberhaus, a commander at the base, said in a statement. "This was a serious breach of security." Andrews is located around 24 kilometers from the White House.

The incident took place a day before U.S. President Joe Biden was set to travel aboard Air Force One from Andrews on Friday evening for a trip to Delaware, in the face of increased security around Washington after the Jan. 6 siege of the U.S. Capitol.

Thousands of National Guard members are still deployed in the capital because of intelligence reports of potential risk for violence at upcoming demonstrations.

Biden's journey to Delaware marks the first time he has travelled onboard Air Force One since taking office on January 20. The plane is only referred to as such when the president is on board.

Intrusion attempts on U.S. military facilities are not uncommon but are rarely successful. In 2018, several military bases across the U.S. faced threatening breach attempts, including Naval Base Kitsap in Washington, Fort Meade in Maryland, and Peterson Air Force in Colorado, a report from Task & Purpose shows.