WASHINGTON — A witness who is cooperating in the special counsel investigation, George Nader, has connections to both the Persian Gulf states and Russia and may have information that links two important strands of the inquiry together, interviews and records show.

Mr. Nader’s ties to the United Arab Emirates are well documented — he is an adviser to its leader — but the extent of his links to Russia had not been previously disclosed.

Mr. Nader, a Lebanese-American businessman, has a catalog of international connections that paved the way for numerous meetings with White House officials that have drawn the attention of the special counsel, Robert S. Mueller III. For example, Mr. Nader used his longstanding ties to Kirill Dmitriev, the manager of a state-run Russian investment fund, to help set up a meeting in the Seychelles between Mr. Dmitriev and a Trump adviser days before Donald J. Trump took office.

Separately, investigators have asked witnesses about a meeting Mr. Nader attended in 2017 with a New York hedge fund manager, where he was joined by Jared Kushner and Stephen K. Bannon, who at the time were both senior advisers to Mr. Trump.

