The F.B.I. has sought to speak with several people who traveled aboard the Qatari-gifted plane that President Trump flew on to Turkey last week, including asking some to turn over their mobile phones, as part of a leak investigation into reporting by The New York Times, according to people with knowledge of the situation.
Among those whom investigators have tried to reach are members of the U.S. Secret Service who accompanied Mr. Trump on the trip, according to one of the people briefed on the matter, who spoke on the condition of anonymity to describe sensitive details about the investigation.
The Secret Service leadership instructed officials working for the agency to refer any outside requests to their lawyers, two of the people said.
The Secret Service did not respond to a request for comment. The F.B.I. declined to comment.
The effort to obtain information from government officials comes after the administration served subpoenas on several Times reporters on Friday night, seeking to compel their testimony this week before a grand jury in Manhattan. The news organization has denounced the move as an attempt to intimidate the journalists.
Administration officials have said that the investigation, which is being led personally by Kash Patel, the F.B.I. director, and the White House chief of staff, Susie Wiles, is aimed at identifying anyone who shared information about security concerns related to the new Air Force One, which was the subject of two Times articles last week.
White House officials on Wednesday declined to address the topic on the record. But in a statement, an official said that leaks “that jeopardize the safety of the president, his staff and the traveling press pool are dangerous and a threat to national security. The White House takes these leaks seriously and will do everything legally to ensure the individual or individuals are caught and it does not happen again.”
CNN reported earlier on new aspects of the investigation.
Mr. Trump flew to a NATO meeting in Turkey last week on the Boeing 747-8, which officials retrofitted and rushed into service at his demand.
While still in Ankara, the Turkish capital, Mr. Trump abruptly announced on social media that he was going to fly “for old time’s sake” on the older model Air Force One, about which he has publicly complained for years, so that he could show the new plane to troops stationed at a military base.
In reality, Mr. Trump was forced to swap planes when he departed because of Secret Service concerns, as The Times first reported on Wednesday.
On Thursday, The Times reported that the Qatari-gifted jet was not equipped with the same defensive capabilities as the older model.
Mr. Trump was furious about the coverage, as The Times previously reported. Mr. Patel scuttled a planned trip to Chicago and spent roughly eight hours at the White House on Friday, running the investigation from there rather than F.B.I. headquarters, a highly unusual decision.
During his confirmation hearing on Capitol Hill on Wednesday, Todd Blanche, the acting attorney general, said he personally authorized the subpoenas.
“We’re not targeting reporters — they’re material witnesses, just like a reporter would be a material witness to a car crash,” Mr. Blanche said, adding, “The question we want to ask them is who provided them with classified national security information.”
The Trump administration is not the first to subpoena reporters. But such a move is usually made as a last resort, and at the very end of an investigation. In this case, the subpoenas were sent out within 48 hours of the publication of the first story and were delivered by F.B.I. agents to the reporters’ homes.
On Wednesday, Democratic senators sharply criticized Jay Clayton, the U.S. attorney in Manhattan, whose office issued the subpoenas, during his separate confirmation hearing to be director of national intelligence.
Mr. Clayton repeatedly declined to discuss specifics of the investigation but defended his decision, saying he had taken all the necessary steps “to protect the First Amendment.”
Senator Kirsten Gillibrand, Democrat of New York, accused Mr. Clayton of flouting “the proper independent legal process” that should have been followed. The decision to serve reporters at their homes, she added, was “rushed, aggressive, with an unnecessary urgency.”
