Special counsel Robert Mueller has requested the Justice Department turn over a range of documents, including some about the dismissal of former FBI director James Comey, it has been reported.
Mr Mueller is currently leading an investigation into whether or not the Trump campaign colluded with the Kremlin, and is also reportedly examining whether Mr Trump himself obstructed justice by asking Mr Comey to drop an investigation into then National Security Advisor Michael Flynn.
Investigators are apparently keen to obtain the emails regarding Mr Comey’s sacking and the decision of Attorney General Jeff Sessions to recuse himself from the matter.
Mr Mueller’s investigative team is interested in exchanges between officials at the Justice Department and the White House, a source told ABC News.
The request was issued in the past month and indicates that Mr Mueller is now demanding documents from the department that is overseeing his investigation.
The special counsel has been examining Russia's influence in the 2016 presidential election and also looking into whether the Trump campaign in particular colluded with the Russians.
Mr Trump’s campaign had begun handing over documents to Mr Mueller in September and a lawyer that represents Mr Trump said the campaign was in “total cooperation” with the special counsel’s investigation.
Mr Mueller’s Russia probe has heated up in recent months. In October, five months after he was appointed to lead the inquiry, he announced 12 charges, including money laundering and conspiracy to defraud the US, against former campaign manager Paul Manafort and associate Rick Gates.
