Intelligence committees in both houses of Congress launched investigations Monday into accusations that Russia interfered in the U.S. presidential election to boost the chances that President-elect Donald Trump would win.
President Barack Obama also ordered a full review by the intelligence community into the allegations.
"The reason that I've called for a review is to really just gather all of the threads of the investigations, the intelligence work that has been done over many months, so that the public and our elected representatives going forward can find ways to prevent this kind of interference from having an impact on the elections in the future."
The probes amounted to an early rebuke of Trump, who over the weekend said the Central Intelligence Agency conclusion was "ridiculous" that Russia engaged in cyberattacks to help him win. He continued to assail the finding Monday.
Even before he assumes power next month, the Republican Trump's mocking of the CIA conclusion about Russian interference on his behalf put him at odds with both of the top Republican lawmakers, Senate Majority Leader Mitch McConnell and House of Representatives Speaker Paul Ryan. They endorsed bipartisan probes conducted by the intelligence committees in each chamber of Congress.
WATCH: McConnell on Russia hacking
"The Russians are not our friends," McConnell said. He added that the investigation should be undertaken with the idea that "the Russians do not wish us well." Ryan said the House probe "should not cast doubt" on Trump's victory, but that foreign interference in a U.S. election was "entirely unacceptable" and Russian involvement "especially problematic."
White House spokesman Josh Earnest said the congressional review "is certainly warranted when you consider the stakes and the consequences."
But Trump spokesman Jason Miller called the CIA conclusion about Russian interference "an attempt to delegitimize President-elect Trump's win."
Clinton camp responds
Trump's election opponent, Democrat Hillary Clinton, has been silent about the Russian hacking allegations. But her campaign manager, John Podesta, on Monday demanded that the administration of President Barack Obama declassify and release all the information it has about Russia meddling in the election.
Clinton won the national popular vote against Trump but lost where it mattered, in the state-by-state contests that decide U.S. presidential elections. Podesta called for release of the intelligence data before electors in the Electoral College vote to formally ratify Trump's victory on December 19.
In a pair of comments on Twitter, Trump questioned why information about the computer hacking was not widely known before the election.
He contended that if Clinton had won the election and Republicans "tried to play the Russia/CIA card, it would be called conspiracy theory.”
He added, "Unless you catch 'hackers' in the act, it is very hard to determine who was doing the hacking. Why wasn't this brought up before election?"
But U.S. officials did in fact publicly accuse Russia of trying to undermine the presidential election in early October, saying intelligence agencies were “confident” Russia directed hacks of the Democratic National Committee that resulted in controversial emails being leaked before the Democratic nominating convention.
Obama spokesman Earnest said, "This was all material that was known by Republican politicians in the Congress that endorsed the president-elect. And how they reconcile their political strategy and their patriotism is something they'll have to explain."
Trump: I don't believe it
Trump's latest remarks came after he told Fox News in an interview aired Sunday that the CIA conclusion about Russian cyberattacks to boost his chances of winning was "just another excuse" by Democrats to explain his stunning upset of Clinton, a former U.S. secretary of state.
"I don't believe it. If you take a look at what [the CIA] said, there's great confusion," Trump said Sunday. "Nobody really knows. They have no idea if it's Russia or China or somebody. It could be somebody sitting in a bed someplace."
Trump told Fox News that he does not oppose Obama's order to review cyberattacks the CIA concluded came from Russia during the lengthy presidential campaign, but said, "You should not just say 'Russia.' You should say other countries also, and maybe other individuals." The CIA said it had "high confidence" that Russia sought to help Trump win.
U.S. intelligence agencies have concluded Russia interfered in the final stretch of the presidential campaign to help Trump win the presidency, and not simply meddle in the U.S. electoral process as previously believed, according to senior Obama administration officials. The conclusion is based to some extent on a finding that Russians hacked the Republican National Committee's computer systems, in addition to those of Democratic organizations, but disclosed only embarrassing emails from the Democrats, via WikiLeaks.
Reince Priebus, the head of the Republican National Committee and Trump's pick for White House chief of staff, told ABC News the party was not hacked.
"The entire report is based on unnamed sources who are perhaps doing something they shouldn't be doing by speaking to reporters or someone talking out of line about something that is absolutely not true," Priebus said Sunday.
Trump's rejection of the CIA conclusion came as Arizona Senator John McCain, the losing 2008 Republican presidential candidate, and three other senators called for the investigation into Moscow's interference in the election, saying that it "should alarm every American." McCain, along with Republican Lindsey Graham and Democrats Jack Reed and Chuck Schumer, said the United States needs to stop "the grave threats that cyberattacks conducted by foreign governments pose to our national security."
Capitol Hill correspondent Michael Bowman contributed to this report