Washington DC – The United States House Judiciary Committee has opened an investigation after reports that journalists and lawmakers were spied on under former president Donald Trump.

It is possible that the cases that recently came to light are isolated incidents, the committee's chairman Jerry Nadler said Monday.

But the cases "raise serious constitutional and separation of power concerns," he said.

Congress must make it "extraordinarily difficult, if not impossible" for the Department of Justice to spy on lawmakers or the media, he said.

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According to media reports, during Trump's time in office, the Department of Justice secretly obtained phone data from reporters and access to data on several Democratic members of Congress.

If this was a systematic effort by the Trump administration to target the political opposition, the full extent of the "gross abuse of power" must be determined and those responsible must be held accountable, Nadler said.

"There are important questions that must be resolved in connection with an effort by the department to obtain records related to Members of Congress and Congressional staff," US Attorney General Merrick Garland said on Monday.

"I have accordingly directed that the matter be referred to the Inspector General and have full confidence that he will conduct a thorough and independent investigation."

The Department of Justice also said Garland met on Monday with representatives from The New York Times, The Washington Post, and CNN and discussed new regulations.

The department reiterated that it would no longer access journalists' data to obtain information about their sources when investigating leaks of confidential information.