The FBI is investigating whether New York Mayor Eric Adams received free upgrades on Turkish Airlines, the country's national carrier, sources familiar with the investigation told ABC News.

       Scrutiny of the flights is part of a wider corruption investigation involving a top Turkish Airlines executive, aides to the mayor and Adams, who previously had his phones and other electronic devices seized.

       MORE: Federal corruption probe scrutinizing possible Turkish links to NYC Mayor Eric Adams' campaign: Sources

       Sources have said at least part of the investigation involves whether donations from Turkey were traded for political favors, including possible pressure exerted on the New York Fire Department after a delay with the operating certificate of the new Turkish consulate.

       A spokesman for the U.S. Attorney's Office for the Southern District of New York declined to comment.

       Mayor Eric Adams speaks during a news conference at the New York City Emergency Manage...Show more ---Show more

       Brittainy Newman/AP

       Adams so far has been accused of no wrongdoing and he has said he has nothing to hide.

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       "As Borough President, the Mayor consistently disclosed his official travel to Turkey, did not receive any improper upgrades and did nothing inappropriate in exchange for an upgrade. Speculation is not evidence. We look forward to a just and timely conclusion to this investigation," Adams' attorney, Brendan McGuire, said in a statement provided to ABC News.

       News of the investigators' interest in possible Turkish Airlines upgrades was first reported by The New York Times.