The US Justice Department agreed to expand its investigation into potential political bias in the FBI's Russia probe to also cover "any irregularities" in FBI tactics, the White House announced on Monday.

It said senior officials from the US Justice Department and the FBI will meet congressional leaders to review highly classified information on the investigation.

The announcements came after US President Donald Trump demanded the Justice Department investigate allegations the FBI planted a mole in his presidential campaign for political reasons.

US media reported last week the FBI had sent an informant to talk to two Trump campaign advisers after receiving evidence of suspicious contact with Russia during the campaign.

Read more: US Democratic Party sues Russia, WikiLeaks, Donald Trump over 2016 election

'Highly inappropriate'

Representative Devin Nunes, head of the House intelligence committee, has demanded the FBI provide information on the source, said to be a US academic, used in the Russia investigation.

"If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action," Deputy Attorney General Rod Rosenstein said in a statement.

But Democrats said special counsel Robert Mueller and his investigation into potential ties between Russia and the Trump campaign should be protected and that confidential FBI information should not be shared with Congress.

Senate Democratic leader Chuck Schumer called the planned meeting highly inappropriate, and said such a meeting must include Democrats, not just Republicans, as a "check on the disturbing tendency of the president's allies to distort facts and undermine the investigation and the people conducting it."

The Justice Department probe was launched in March, partly at the request of Congressional Republicans, to review whether FBI and Justice Department officials had abused their powers to justify monitoring Carter Page, a former campaign adviser to Trump.

Read more: US Congressional panel clears Trump campaign of collusion with Russia

aw/gsw (AP, Reuters)