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. Mr Trump has not been accused of any wrongdoing.
In March, the US imposed sanctions on 19 Russians, including 13 people charged by Mr 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.
Who is Van der Zwaan?
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.
"What I did was wrong. I apologise to this court, and I apologise to my wife," he said at the hearing.
What were the accusations?
According to court documents, Van der Zwaan "wilfully and knowingly" made false statements to investigators while answering questions about a report prepared in 2012 by his former law firm for the Ukrainian Ministry of Justice on the trial of Yulia Tymoshenko.
Ms Tymoshenko, a former Ukrainian prime minister, was jailed in 2011 over a gas deal with Russia, in charges she said were politically motivated.
The report prepared by Skadden was used to defend Ukraine's then pro-Russia President Viktor Yanukovych from international criticism over the jailing of Ms Tymoshenko, a bitter rival who he defeated to become president in 2010.
Mr Mueller's indictment said Van der Zwaan "deleted and otherwise did not produce emails sought by the special counsel's office" and made a false statement about when he was last in contact with Mr Gates and "Person A", who has not been identified but is described as a long-term business associate of Mr Gates and Mr Manafort.
US media have identified Person A as a former Russian intelligence operative.
Mr Gates and Mr Manafort have been hit with a number of charges, including conspiracy to launder money and acting as "unregistered agents" of Mr Yanukovych and his party.
Mr Manafort has denied all charges against him. Mr Gates has admitted conspiracy and lying to investigators in a plea deal.
A milestone - but Manafort is the one to watch
Analysis by BBC North America correspondent Anthony Zurcher
Special counsel Robert Mueller has brought charges against 19 individuals and he has obtained five guilty pleas. Now, with Alex van der Zwaan's 30-day prison sentence, he has closed his first case.
The lawyer's ordeal appears somewhat tangential to the central thrust of Mr Mueller's investigation, but the special counsel's office made clear that lying to government investigators must have consequences.
In addition, information prosecutors obtained from him may have been key to securing the co-operation of former Trump campaign and transition aide Rick Gates, who could in turn help seal former Trump campaign chair Paul Manafort's legal fate.
For the moment, at least, Mr Manafort continues to be the central figure in this investigation. Based on information released by Mr Mueller's office on Monday night, his ties to Russia - while he was involved with the Trump campaign - are squarely under the microscope.
While Van der Zwaan's sentencing is a milestone in Mr Mueller's inquiry, Paul Manafort is the biggest and most important domino currently standing.
Who else has been charged by Mr Mueller?
Nineteen people - including Mr Manafort and Mr Gates - have been indicted by the special counsel:
- Michael Flynn, a former US national security adviser, pleaded guilty to lying to the FBI over meetings he had with the Russian Ambassador, Sergei Kislyak
- George Papadopoulos, a former Trump campaign adviser, admitted lying to the FBI about his contacts with Russians
- In March, 13 Russians were charged with tampering in the 2016 US election and a California man, Richard Pinedo, admitted an identity theft charge
Mr Trump has insisted there was no collusion. Moscow has rejected US intelligence claims of interference.