President Trump said on Saturday that he had fired Michael T. Flynn, his first national security adviser, because he lied not just to the vice president but also to the F.B.I.

The president has long asserted that he fired Mr. Flynn in February, less than a month after he took office, because Mr. Flynn had lied to Vice President Mike Pence over whether he talked with the Russian ambassador, Sergey I. Kislyak, about sanctions imposed on Russia by President Barack Obama.

By saying on Twitter on Saturday that Mr. Flynn’s lies to the F.B.I. had also contributed to his firing, some took that to mean that Mr. Trump was acknowledging that he had known in February that Mr. Flynn was untruthful with the bureau’s agents. Any such admission would be important in light of Mr. Trump’s effort that month to persuade the bureau’s director at the time, James B. Comey, to drop the investigation into Mr. Flynn.

But White House officials said that Mr. Trump was merely acknowledging what had happened the day before: Mr. Flynn’s guilty plea for lying to the F.B.I. about his conversations with Mr. Kislyak.