Washington: The Dutch son-in-law of one of Russia's richest men has been sentenced on 30 days in prison and a $US20,000 ($26,000) fine for lying to Special Counsel Robert Mueller's investigators about contacts with an official in President Donald Trump's 2016 campaign.

Alex van der Zwaan, a lawyer who once worked closely with Trump's former campaign chairman Paul Manafort, was also sentenced to two months of supervised release by US District Court Judge Amy Berman Jackson. 

He had pleaded guilty on February 20 as Mueller intensified his investigation into potential collusion between the president's campaign and Russia.

In pleading guilty, he admitted he lied to FBI agents about previous communications with Rick Gates, a Manafort protege who held a senior position in the Trump campaign, and that he also withheld and deleted emails.

"What I did was wrong. I apologise to this court, and I apologise to my wife," van der Zwaan said at the sentencing hearing.