He is scheduled for sentencing on April 3.

Until then, the FBI will keep van der Zwaan's passport, and he won't be allowed to travel outside the US. Van der Zwaan must stay in Washington, DC, and Manhattan, where his attorneys are based, until his sentencing, and a judge must review his requests to travel elsewhere within the United States. His sentencing is set at a relatively early date, because his wife is facing a difficult pregnancy in London, his defense attorney told the judge.

His wife, Eva Kahn, the daughter of Russian billionaire German Khan, is due in August.

Van der Zwaan becomes the fourth guilty plea in the Mueller investigation after Trump campaign aide George Papadopoulos and former national security adviser Michael Flynn pleaded guilty to lying to investigators last year, and an online supplier of fake usernames pleaded guilty to identity fraud last week. Mueller has also indicted 13 Russians for their work to influence the 2016 presidential election through online social media.

Unlike other defendants, Van der Zwaan did not enter into an ongoing cooperation agreement with the special counsel's office.

Van der Zwaan's conversation with the special counsel's office in which he allegedly lied happened three days after Manafort and Gates were charged with crimes related to their work for Ukrainian politicians and other business. Both have pleaded not guilty.

In early November, prosecutors questioned van der Zwaan on his work with international law firm Skadden Arps. They were investigating Manafort's, Gates' and other individuals' compliance with the Foreign Agents Registration Act, which governs foreign lobbying and propaganda work for foreign governments in the US, and wanted to know who paid for a Ukrainian report on the trial of a former prime minister and how it was paid for, prosecutors said in court Tuesday.

Van der Zwaan spoke with the special counsel's office a second time in early December to confess to his inaccuracies and what he knew, according to prosecutors' statements in court and a plea agreement released Tuesday.

Ukrainian work

Manafort arranged for the law firm to help the Ukrainian minister of justice in 2012 report on the trial of Yulia Tymoshenko, a former Ukrainian prime minister opposed to Manafort's clients.

At least one public relations firm worked on the rollout of Skadden's report with Gates and Manafort. In total, Manafort and Gates funneled $4 million to facilitate the rollout of the Ukrainian report in the US and Europe, prosecutors said Tuesday.

Van der Zwaan worked with Manafort, Gates and the public relations firm in 2012 to fashion a public spin on the Ukrainian report without his law firm's knowledge.

He had given a public relations firm a copy of the report before its public release, and handed Gates talking points about the report that would help the Ukrainian clients, against the direction of a more senior lawyer at the Skadden law firm, according to court documents and prosecutors' descriptions in court.

Tymoshenko, the subject of the report, is one of the top political rivals of former Ukrainian President Viktor Yanukovych, a Russian sympathizer who used Manafort and Gates as political consultants for more than a decade. After Yanukovych narrowly defeated Tymoshenko in the 2010 presidential election, she was jailed on charges of corruption that were seen by many as being politically motivated.

Skadden produced a report -- intended to be independent -- that said the process was legal. She was freed after Yanukovych's ouster in 2014.