The FBI have raided the offices and home of Michael Cohen, the long-time personal lawyer for US President Donald Trump.
The 51-year-old is under investigation over possible bank fraud, wire fraud and campaign finance violations, according to people close to the case.
Cohen has been at the centre of a controversy surrounding payment to porn star Stephanie Clifford, known as Stormy Daniels.
Daniels has alleged that she had sex in 2006 with Mr Trump and was paid money shortly before the 2016 election to keep quiet about it.
Stephen Ryan, Cohen's lawyer, confirmed that a raid had taken place and that certain "communications" had been seized.
"I have been advised by federal prosecutors that the New York action is, in part, a referral by the Office of Special Counsel, Robert Mueller," Ryan said in a statement.
"The decision by the U.S. Attorney's Office in New York to conduct their investigation using search warrants is completely inappropriate and unnecessary," he added.
Mueller is investigating allegations that Russia meddled in the U.S. presidential election in 2016, and investigating possible collusion between Russia and the Trump campaign.
Russia has denied allegations that it interfered in the election, and Trump and the White House have repeatedly said there was no collusion.
Ryan said in his statement that Cohen has cooperated with authorities and turned over thousands of documents to congressional investigators for their own probes into Moscow's alleged efforts to influence the U.S. election.
A source said the FBI seized emails, tax documents and business records,
U.S. President Donald Trump described the raid as a disgraceful action and a total witch hunt.
Speaking to reporters at the White House, Trump called Special Counsel Robert Mueller's team the most biased group of people and reiterated his view that Attorney General Jeff Sessions should not have recused himself from overseeing Mueller's probe of alleged Russian meddling in the U.S. election.