The top Democrat on the US Senate panel investigating Russian election meddling warned that President Donald Trump should not pardon associates who could be implicated in a separate criminal probe into the matter.

"The possibility that the president is considering pardons at this early stage in these ongoing investigations is extremely disturbing," said Warner.

"Pardoning any individuals who may have been involved would be crossing a fundamental line.”

Mark Warner's statement followed a report by the Washington Post that Trump recently discussed his presidential pardon power with advisers, including asking about pardoning aides, relatives and himself.

Citing unnamed sources familiar with White House deliberations, the newspaper said that Trump's lawyers have likewise discussed pardon issues and researched ways to discredit the Justice Department investigation led by special counsel Robert Mueller.

The New York Times similarly reported that Trump's lawyers were discussing how to inhibit the criminal probe.

John Dowd, a lawyer for Trump, said the Post's story was not true.

“The president’s lawyers are cooperating with special counsel Robert Mueller on behalf of the president,” he said.

White House press secretary Sarah Sanders referred reporters to Dowd's statements when asked where the president stands on the issue of pardons.

"The president maintains pardon powers, like any president would. But there are no announcements or planned announcements on that front whatsoever," Sanders said.

The president's son, Donald Trump Jr, and Jared Kushner, the president's son-in-law, are both believed to be part of the investigation based on their contacts with Russia during the campaign.

Former campaign manager Paul Manafort and top campaign advisor Michael Flynn, who briefly served as White House national security adviser, are under investigation for similar contacts.

Trump Jr, Kushner and Manafort all participated in a June 2016 meeting with a Russian lawyer who had promised through an intermediary to pass along damaging information from the Russian government about Democratic presidential candidate Hillary Clinton.

The lawyer failed to deliver information and instead lobbied them on US-Russian relations, Trump Jr said last week.

Mueller's office recently formally asked the White House to preserve all documents relating to the June 2016 meeting, US broadcaster CNN reported Friday, citing a source who had seen the letter and read parts of it to a CNN reporter.

The request covers any documents or communications including notes, emails, text messages and voicemails, related to what was discussed in the meeting or decisions made as a result of the meeting.

The letter said that the special counsel's office "is investigating the Russian government's efforts to interfere in the 2016 presidential election, including any links or coordination between the Russian government and individuals associated with the campaign of Donald Trump."

Any information about the June 2016 meeting "is relevant to the investigation," the letter said.

White House lawyers this week notified staff of the preservation request, CNN reported, citing a second source.

- dpa

Investigator asks White House to save Russian meeting documents