The first person has been jailed as part of the FBI inquiry into alleged collusion between Donald Trump’s presidential campaign team and Russia.
Dutch lawyer Alex van der Zwaan, 33, was sentenced to 30 days in prison for lying to investigators about contacts with ex-Trump aide Rick Gates.
He struck a plea deal in February.
Van der Zwaan is the son-in-law of one of Russia’s richest men and was the 19th person to be charged by special counsel Robert Mueller.
The indictment against him did not refer to the 2016 election campaign. Trump has not been accused of any wrongdoing.
In March, the US imposed sanctions on 19 Russians, including 13 people charged by Mueller’s inquiry, over accusations of interference in the 2016 election and alleged cyber-attacks.
In court on Tuesday, Van der Zwaan was also fined $20,000 and sentenced to two months of supervised release.
The Dutchman is a London-based lawyer who formerly worked at international law firm Skadden, Arps, Slate, Meagher & Flom.
The firm, which is co-operating with the investigation and which fired him last year, worked with former Trump campaign chief Paul Manafort and his ex-colleague Mr Gates at a time when they were both political consultants in Ukraine.
Van der Zwaan, who speaks French and Russian and graduated from King’s College London in 2006, is married to the daughter of Russian billionaire German Khan.
His wedding to art critic Eva Khan featured in Russian Tatler magazine last year. His lawyers had asked the US District Court judge in Washington to let him return to London by August, when his wife is due to give birth.
German Khan controls Alfa Group, one of Russia’s largest investment groups. Alfa Bank, which he co-founded, is the largest non-state owned bank in Russia, according to Forbes.
Van der Zwaan admitted to making false statements to the special counsel’s office in November 2017 as part of a plea deal reached in February.