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.

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

More to come