House Speaker Paul Ryan on Thursday backed key lawmakers' statements that no evidence supports President Donald Trump 's claim that Trump Tower was wiretapped before the 2016 election.

"The intelligence committees in their continuing, widening ongoing investigation of all things Russia, got to the bottom — at least so far with respect to our intelligence community — that no such wiretap existed," Ryan told reporters.

In a separate statement later Thursday, the top Republican and Democrat on the Senate Intelligence Committee said that based on evidence they have, they "see no indications that Trump Tower was the subject of surveillance by any element of the United States government either before or after Election Day 2016."

On Wednesday, House Intelligence Committee Chairman Devin Nunes, R-Calif., and ranking member Adam Schiff, D-Calif., both said they had not seen evidence to back Trump's explosive allegation. Trump did not cite any specific information when he accused former President Barack Obama of tapping his phones in a series of tweets earlier this month.

"I don't think there was an actual tap of Trump Tower," Nunes said.

The White House has gradually shifted its explanation of Trump's tweets since he first made them. Press secretary Sean Spicer this week tried to cast Trump's tweets as meaning broader surveillance beyond a physical wiretap of Trump Tower, citing the quotes around "wiretapping" in one statement.

However, Trump did not use quotes in all of his tweets.

In a Fox News interview Wednesday, Trump contended that the word wiretap "covers a lot of different things." He said "some very interesting things" may surface in the coming weeks, without specifying what those would be.

The White House previously asked Congress to add Trump's wiretapping claims to its ongoing probes into the extent of Russian influence on the 2016 U.S. election. The American intelligence community concluded that Moscow meddled, first aiming to harm then-candidate Hillary Clinton and then developing a preference for Trump.

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