WASHINGTON (Reuters) - The leaders of the U.S. Senate Intelligence Committee issued a bipartisan statement on Thursday rejecting President Donald Trump’s assertion that the Obama administration tapped his phones during the 2016 presidential campaign.

The top Republican in Congress, House of Representatives Speaker Paul Ryan, added his voice to a growing chorus of lawmakers saying there was no sign of a wiretap.

In a testy briefing with reporters, White House spokesman Sean Spicer forcefully defended the president, citing news reports of intelligence collection on possible contacts between Trump associates and Russia in the presidential campaign.

“There is no question that there were surveillance techniques used throughout this,” Spicer said.

The Republican president, without providing evidence, has accused his predecessor, Democrat Barack Obama, of wiretapping him near the end of the campaign. An Obama spokesman said that was “simply false.”

“Based on the information available to us, we 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,” Richard Burr, the Republican chairman of the Senate Intelligence Committee, and Senator Mark Warner, the committee’s Democratic vice chairman, said in a statement.

Ryan also said there was no evidence of surveillance.

“The point is, 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 - that no such wiretap existed,” the House speaker told reporters.

‘HE STANDS BY IT’

U.S. President Donald Trump walks from Marine One as he returns to the White House in Washington. REUTERS/Joshua Roberts

Pressed at the White House briefing on whether Trump would back down from his wiretap accusations, Spicer said: “He stands by it.”

Spicer also chastised the media for focusing so much attention on comments disparaging Trump’s claim about surveillance. He said reporters had not focused enough on comments from officials denying evidence of any collusion between Russia and the Trump campaign.

The Russian government has rejected an accusation by U.S. intelligence agencies that it worked to influence the election in Trump’s favor by hacking computer systems, among other methods.

Trump has been dogged by allegations that his associates had ties to Russian officials. Trump fired his national security adviser, Michael Flynn, last month after he failed to disclose contacts with Russia’s ambassador before Trump took office on Jan. 20.

An official familiar with the investigations by Congress and intelligence and law enforcement agencies said investigators had looked as aggressively and thoroughly as they could for evidence of any spying on Trump or his associates but had found none.

On March 4, six weeks after he took over from Obama, Trump made the wiretap accusations in a Twitter post.

“How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!,” Trump wrote.

At least four congressional committees included the startling accusation in their investigations of possible Russian meddling in the election campaign and Russian ties to Trump and his associates.

On Wednesday, House of Representatives Intelligence Committee Chairman Devin Nunes, a Republican, and top Democrat Adam Schiff told reporters they had seen no evidence that Trump Tower was tapped and said they would ask Federal Bureau of Investigation Director James Comey about the issue during a public hearing on Monday.

On March 9, Comey briefed Nunes, Schiff, Ryan, Burr, Warner and three other top congressional officials on the same intelligence.

Trump appeared to back away from his accusation of wiretapping in a Fox News interview on Wednesday night.

“But wiretap covers a lot of different things. I think you’re going to find some very interesting items coming to the forefront over the next two weeks,” Trump said.