WASHINGTON — The finances and business dealings of Jared Kushner, President Trump’s son-in-law and adviser, are being investigated by special counsel Robert S. Mueller III is as part of probes into Russia’s interference in the 2016 presidential election, officials familiar with the matter told The Washington Post.

FBI agents and federal prosecutors are also examining other Trump associates, including former national security adviser Michael Flynn, former campaign chairman Paul Manafort and Carter Page, a foreign-policy adviser for Trump’s campaign.

Investigators had been analyzingmeetings that Kushner held with Russians in December — first with Russian ambassador Sergey Kislyak, and then with Sergey Gorkov the head of a state-owned Russian development bank. Kushner suggested establishing a secure communications line between Trump officials and the Kremlin at a Russian diplomatic facility during a December meeting with Kislyak, according to U.S. officials who reviewed intelligence reports describing Kislyak’s account.

The White House has said that the subsequent meeting with the banker was a pre-inauguration diplomatic encounter, unrelated to business matters.

The Russian bank, Vnesheconombank, which has been the subject of U.S. sanctions following Russia’s annexation of Crimea, has said the session was held for business reasons because of Kushner’s role as head of his family’s real estate company.

The meeting occurred as Kushner’s company was seeking financing for its troubled $1.8 billion purchase of an office building on Fifth Avenue in New York, and it could raise questions about whether Kushner’s personal financial interests were colliding with his impending role as a public official.