Following demands by President Donald Trump for the Justice Department to investigate his claim that his campaign had been "infiltrated or surveilled" by the FBI, the agency on Monday directed the Inspector General to probe those accusations.

"The Department has asked the Inspector General to expand the ongoing review of the FISA application process to include determining whether there was any impropriety or political motivation in how the FBI conducted its counterintelligence investigation of persons suspected of involvement with the Russian agents who interfered in the 2016 presidential election," Department of Justice spokeswoman Sarah Isgur Flores said in a statement.

"As always, the Inspector General will consult with the appropriate U.S. Attorney if there is any evidence of potential criminal conduct," she added.

Deputy Attorney General Rod Rosenstein, who oversees special counsel Robert Mueller's investigation into Russian interference in the 2016 race and the Trump campaign's possible involvement with Moscow, added that "if anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action."

Trump met Monday afternoon with Rosenstein, as well as FBI Director Christopher Wray, White House Chief of Staff John Kelly and Dan Coats, the director of national intelligence to discuss their response to congressional requests on a range of topics, White House Press Secretary Sarah Sanders told NBC News.

Sanders credited the session with Rosenstein's decision to ask the inspector general's office to expand its probe, even though DOJ had announced that move earlier in the day, before the meeting.

She added that White House Chief of Staff Kelly planned to set up a meeting with the FBI, DOJ and DNI together with congressional leaders "to review highly classified and other information they have requested."

The Justice Department's internal watchdog is already examining Republican complaints of FBI misconduct in the early stages of the Russia investigation.

Inspector General Michael Horowitz announced an investigation in March at the request of Attorney General Jeff Sessions and congressional Republicans. Sessions and the lawmakers had urged Horowitz to review whether FBI and Justice Department officials abused their surveillance powers by using information compiled by Christopher Steele, a former British spy, as part of the basis to justify monitoring Carter Page, a former campaign adviser to Trump.

The Justice Department's latest announcement came after Trump on Sunday demanded an investigation.

I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes - and if any such demands or requests were made by people within the Obama Administration! — Donald J. Trump (@realDonaldTrump) May 20, 2018

Democrats criticized Trump for interfering with the Justice Department.

"For months, @realDonaldTrump has insulted & tried to discredit the men & women at FBI & DOJ in self-serving attempts to distract from the Trump-Russia scandal," tweeted House Minority Leader Nancy Pelosi, D-Calif. "His conspiratorial fantasies must not be allowed to undermine the proper function of our justice system."

Sen. Dianne Feinstein, D-Calif, posted, "The Justice Department is not an arm of the White House. The Justice Department is independent and serves the American people."

"Its job is to follow the facts and the law. Law enforcement investigations must be initiated and carried out free from political interference," Feinstein wrote.

The New York Times reported on Saturday that at least one government informant met several times with Page and George Papadopoulos, another former foreign policy adviser on Trump's campaign.

The Times, citing current and former FBI officials, reported that the informant talked to Page and Papadopoulos because they had suspicious contacts linked to Russia. Papadopoulos was charged last year in Mueller's investigation and pleaded guilty to lying to the FBI. He has agreed to cooperate with prosecutors.

Trump had been tweeting similar allegations for days. On Friday, he accused the Department of Justice of putting a "spy" inside his presidential campaign as part of an effort to frame him for crimes he says he "didn't commit."

"'Apparently the DOJ put a Spy in the Trump Campaign. This has never been done before and by any means necessary, they are out to frame Donald Trump for crimes he didn't commit,'" Trump tweeted Friday, quoting Fox Business Network anchor David Asman. "Really bad stuff!"

Later, the president weighed in again, saying that if the reports are true, it would be the "all time biggest political scandal."

Rudy Giuliani, one of Trump's lawyers, said on Friday that the president's legal team had been told about an informant "off the record," but added that he didn't know if the information was correct.

A day earlier — on the anniversary of the appointment of Mueller — Trump tweeted that then-President Barack Obama had "spied on the Trump campaign," an apparent reference to an allegation that Andrew McCarthy, a former federal prosecutor and assistant U.S. attorney, had made at the time on Fox News.