WEST PALM BEACH, Fla. — The Secret Service detained a man late on Saturday after he drove his car up to a checkpoint near the White House and said he had a bomb, according to the police, an episode that resulted in his arrest and in security on the grounds being beefed up.

President Trump, who was spending the weekend at his estate in Palm Beach, Fla., was not in the White House at the time, but the Secret Service increased its “posture of readiness” in response to the episode, a spokesman said.

The intrusion came just days after a man made his way onto the White House grounds while Mr. Trump was inside. The intruder in that episode roamed the grounds undetected for about 17 minutes as Secret Service agents failed to respond to several alarms.

In Saturday’s episode, the intruder stopped his car at the White House checkpoint just after 11 p.m. and got out, declaring, “There’s a bomb in the trunk,” as he appeared to clasp something in his hand, according to a report issued by the Metropolitan Police Department.