WASHINGTON • The US Secret Service has bolstered security at the White House after a man was arrested making threats at one of its checkpoints, a third such security scare in just over a week.

CNN reported that the man made a threat claiming he had a bomb in his car, and that he was immediately arrested and the car in which he was travelling seized.

President Donald Trump was away in Florida at the time.

"On March 18, 2017, at approximately 11.05pm, an individual drove a vehicle up to a Secret Service checkpoint located at 15th Street and E Street NW," a Secret Service spokesman said in the latest of a series of White House security concerns.

"Upon contact with the individual, US Secret Service Uniform Division Officers detained the individual and declared his vehicle suspicious. In accordance with proper protocols, Secret Service personnel increased their posture of readiness," he added.

Just hours earlier, a person was arrested after jumping over a bike rack in an apparent bid to reach the fence outside the White House, the United States Secret Service said.

The individual was detained immediately and criminal charges are pending, the agency said in a statement, without identifying the suspect.

The arrest came about a week after a more serious incident that called into question security outside the White House.

Just before midnight on March 10, a man scaled three barriers outside the White House - a perimeter fence, a vehicle gate and then another fence - and walked around the grounds of the executive mansion for 16 minutes before being arrested.

At that time, Mr Trump was inside the building.

"(Homeland Security chief John) Kelly told me that this person... went undetected, was able to get up next to the White House, hide behind a pillar, look through a window, and rattle the door handle," Republican Congressman Jason Chaffetz told news channel CNN.

The White House has seen a string of high-profile trespassing incidents in recent years.

In one notable incident in 2014, while Mr Barack Obama was president, an army veteran described as mentally disturbed made it into the White House grounds, sprinted across the lawn and entered the building with a knife in his pocket before being tackled and arrested.

AGENCE FRANCE-PRESSE