The FBI has raided the offices of Michael Cohen, the long-time personal lawyer for US President Donald Trump, BBC reports.
Law enforcement acted on a "referral" from Special Counsel Robert Mueller, who is investigating suspected Russian meddling in the 2016 election.
Officials in New York seized "privileged communications" between Mr Cohen and his clients, his lawyer said in a statement after the raid.
Documents regarding a payment to a porn actress were also seized, US media say.
Mr Cohen has come under increasing public scrutiny since he admitted to making a $130,000 (£92,000) payment to adult film star Stormy Daniels, whose real name is Stephanie Clifford, just days before the 2016 presidential election.