President-elect Donald Trump has rejected as "ridiculous" a CIA assessment that Russian hackers tried to sway the election in his favour.
He told Fox News the Democrats were putting out the reports because they were embarrassed at the scale of the election defeat.
Russian officials have repeatedly denied the hacking accusations.
Mr Trump said it might have been Russia but it was impossible to know.
"They have no idea if it's Russia or China or somebody sitting in a bed some place," he said.
President Barack Obama has ordered a complete review of the hacks, which targeted emails at the Democratic Party and the emails of a key aide to presidential nominee Hillary Clinton.
The contents of the emails, passed to Wikileaks and posted online, were embarrassing to the Democrats and shook up the presidential campaign.
Senior Republicans have now joined Democrats in calling for a full investigation.
Republican Senator John McCain, chairman of the Senate Armed Services Committee, said in a joint statement on Sunday with top Democrats that the CIA's report "should alarm every American".
He said in an interview that the congressional investigation should be more thorough than the one ordered by the White House.
In October, US government officials pointed the finger at Russia, accusing it of meddling in the campaign to undermine the electoral process.
But on Friday, the intelligence community went further when US media reports said the CIA had "high confidence" that Russians were trying to influence the election in Mr Trump's favour.
Russians had hacked the Republican party but chose not to reveal the contents of what they found, the reports said.
But Mr Trump told Fox News Sunday: "I think it's ridiculous. I think it's just another excuse. I don't believe it."
He said the Democrats were behind the news reports, not the CIA, because they suffered such a big defeat.
While backing the Obama review, the president-elect warned that it should not pin the blame solely on Russia but on other countries or individuals too.
Republican party spokesman Sean Spicer said the party had not been hacked and the intelligence report was wrong.