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.

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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.

“This is a test,” the man said as a Secret Service officer detained him and took him to the ground, according to the report.

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The man was charged with making false bomb threats and the unauthorized use of a vehicle, which had been reported stolen, the report said. The police identified him as Sean Patrick Keoughan, 29, of Roanoke, Va.

Earlier on Saturday, another man was arrested after jumping over bicycle-rack-style barricades into a restricted area outside the White House fence on Pennsylvania Avenue, where he stood “yelling nonsensical statements,” according to a police report. The police identified him as William Bryant Rawlinson, 58, of Silver Spring, Md.

Neither episode was as serious as the one on March 10, in which Jonathan Tuan-Anh Tran, 26, of Milpitas, Calif., breached the outer perimeter of the White House near the Treasury building, the authorities said.

At the time, Mr. Tran was carrying a backpack with two cans of pepper spray, a book by Mr. Trump, a letter to the president and other items, the authorities said. He was able to elude multiple layers of security before being stopped near the entrance at the South Portico.

That episode prompted Representative Jason Chaffetz, Republican of Utah and the chairman of the House Committee on Oversight and Government Reform, to suggest that the Secret Service’s security measures were still inadequate two and a half years after a series of lapses tarred the agency and led to a major upheaval.

Mr. Tran’s ability to remain uncaught for so long recalled an embarrassing episode for the Secret Service in September 2014 in which Omar J. Gonzalez, a fence jumper armed with a knife, managed to run through the ceremonial East Room of the White House before being apprehended.