An NBC News internal investigation into Brian Williams has examined a half-dozen instances in which he is thought to have fabricated, misrepresented or embellished his accounts, two people with inside knowledge of the investigation said.

The investigation includes at least one episode that was previously unreported, these people said, involving statements by Mr. Williams about events from Tahrir Square in Cairo during the Arab Spring.

The investigation, conducted by at least five NBC journalists, was commissioned early this year after Mr. Williams was forced to apologize for embellishing an account of a helicopter episode in Iraq in 2003. He was subsequently suspended for six months from his anchor position on the “NBC Nightly News.” The inquiry is being led by Richard Esposito, the senior executive producer for investigations, for the news division.

The review of Mr. Williams’s reporting is not finished and no final conclusions have been reached. When completed, it is expected to form the basis for a decision on whether to bring him back. It is not clear when that decision will be made.