WASHINGTON (Reuters) - U.S. House Intelligence Committee Chairman Adam Schiff on Friday warned the FBI and U.S. spy agencies that President Donald Trump is trying to “politicize” U.S. intelligence and law enforcement.

FILE PHOTO - House Intelligence Committee Chairman Rep. Adam Schiff (D-CA) arrives for an address by NATO Secretary General Jens Stoltenberg to a joint meeting of Congress in the House Chamber on Capitol Hill in Washington, U.S., April 3, 2019. REUTERS/Carlos Barria

Schiff criticized Trump for giving Attorney General William Barr “sweeping” powers to declassify or downgrade the secrecy of government reporting while conducting what the Justice Department is calling a “review” of “intelligence activities” related to the 2016 U.S. presidential election campaign.

In letters to agency heads, Schiff said May 23 orders from Trump telling them to help with Barr’s review was “an effort by the President and the Attorney General to politicize the IC (intelligence community) and law enforcement, to deligitimize a well-founded investigation into the President, and to attack the President’s political enemies.”

Schiff sent his letters, which Reuters saw, to the directors of National Intelligence, the FBI, CIA and National Security Agency.

He asked them to keep his panel informed about Barr’s review; provide documents produced for it; and tell the committee about any moves by Barr to declassify material over agency objections.

Spokespeople for NSA and the Director of National Intelligence said their agencies received Schiff’s letter but had no further immediate comment. An FBI spokeswoman and CIA spokesman declined to comment.

U.S. Special Counsel Robert Mueller on Wednesday said his investigation found that Russia interfered in the 2016 U.S. presidential election, but did not produce sufficient evidence of a conspiracy between the Trump campaign and Moscow.

Trump has repeatedly accused senior national security aides of spying on his campaign.

“My Campaign for President was conclusively spied on. Nothing like this has ever happened in American Politics. A really bad situation. TREASON means long jail sentences, and this was TREASON!”, the president tweeted in mid-May.

Advisors to former President Barack Obama, who was in office during the campaign, have denied Trump’s accusations.

On Friday, Barr defended his review. “There were counterintelligence activities undertaken against the Trump campaign. And I’m not saying there was not a basis for it, ... but I want to see what that basis was and make sure it was legitimate,” he told CBS News.

Reuters reported on Tuesday that one key witness who is expected to refuse to cooperate with the review is former British spy Christopher Steele, author of a controversial “dossier” about alleged Trump interactions with Russia.