WASHINGTON (Reuters) - U.S. House Speaker Paul Ryan said on Wednesday that President Donald Trump should not pardon himself, becoming the second Republican leader in Congress to balk at the president’s assertion that he had “absolute” power to do so.

Ryan also dismissed another of Trump’s contentions - that the FBI and Justice Department planted an informant in his 2016 presidential campaign. He said he agreed with the assertion by U.S. Representative Trey Gowdy, the Republican chairman of the House Oversight Committee, that federal authorities had acted properly.

“I think Chairman Gowdy’s initial assessment is accurate, but we have more digging to do,” Ryan said.

Ryan, who is not seeking re-election, had a strained relationship with Trump during the campaign but has avoided taking a confrontational approach with him since he took office.

Asked whether Trump can legally pardon himself, Ryan told reporters at the U.S. Capitol: “I don’t know the technical answer to that question but obviously he shouldn’t. No one is above the law.”

Trump made the pardon assertion in a series of Twitter posts on Monday in which he criticized federal Special Counsel Robert Mueller’s criminal probe of whether his 2016 presidential campaign colluded with Russia to sway the election.

“As has been stated by numerous legal scholars, I have the absolute right to PARDON myself, but why would I do that when I have done nothing wrong?” Trump said.

In another tweet he called Mueller’s appointment “totally UNCONSTITUTIONAL.”

The comments came as Mueller’s investigation, which includes possible illegal obstruction of the Russia probe by the president, entered its second year.

Trump denies he colluded with the Russians or obstructed justice and calls Mueller’s investigation a “witch hunt.”

On Tuesday, the Senate’s Republican leader, Mitch McConnell, also discouraged talk of a self-pardon by Trump.

“Let me just tell you that from - from my perspective - I don’t think the president needs any advice on pardoning himself,” McConnell said. “He obviously knows that would not be something that he would or should do.”

Trump’s suggestion that he could legally pardon himself followed a New York Times report on Saturday that his personal lawyers argued in a memo to Mueller that the president could not have obstructed justice because he has vast authority over all federal investigations.

In an interview with Reuters on Sunday, Trump lawyer Rudolph Giuliani played down the possibility of a Trump self-pardon.

“He’s not going to do it. He’s not going to pardon himself. If he did, he’d be impeached so fast,” Giuliani said.