Prosecutors in New York have convened a special grand jury as part of a two-year investigation into Donald Trump’s business dealings.
According to news first reported in The Washington Post, the grand jury will meet three days a week for six months and could eventually be asked to consider returning indictments.
Mr Trump is being investigated by Manhattan District Attorney Cyrus Vance Jr for matters including property valuations, hush-money payments to women on his behalf, and employee compensation.
Issues under investigation include Mr Trump’s relationship with his lenders, a land donation made to qualify for an income tax deduction, and tax write-offs claimed by the Trump Organisation.
In recent weeks the investigation appears to have focused on Mr Trump’s finance chief Allen Weisselberg.
His former daughter-in-law Jen Weisselberg, who is cooperating with the inquiry, has passed on documents helping investigators look at whether some Trump employees might have been given unofficial benefits such as housing or school tuition.
In February the US Supreme Court cleared the way for Mr Vance to enforce a subpoena on Mr Trump’s accountants, releasing eight years of tax returns for the former president, and his businesses.
The documents are not expected to be made public, as they are protected by grand jury secrecy rules.
Mr Trump has said the investigation is a “witch hunt”, adding last week that he is being “unfairly attacked and abused by a corrupt political system”.
He has also said that he is the victim of a plot to stop him from seeking the presidency again.