Senior Republicans in Congress have said they will support further investigation of findings that Russian hackers meddled in the US election.
House Speaker Paul Ryan and Senate Majority leader Mitch McConnell said any foreign intervention in the polls was unacceptable.
President-elect Donald Trump has repeatedly poured scorn on the claims, made by US intelligence.
The CIA concluded on Friday that Russia's motive was to help Mr Trump.
Mr McConnell and Mr Ryan said their respective intelligence committees would investigate the allegations.
"Any foreign breach of our cyber-security measures is disturbing and I strongly condemn any such efforts," Senator McConnell told reporters, adding that "the Russians are not our friends".
Mr Ryan echoed these remarks, but warned against exploiting the work of the intelligence community for "partisan purposes".
"As we work to protect our democracy from foreign influence, we should not cast doubt on the clear and decisive outcome of this election," he said in a statement posted on Twitter.
The remarks came amid suggestions by Mr Trump that the claims were politically motivated.
On Sunday he told Fox News the Democrats were disseminating the "ridiculous" hacking reports because they lost the election.
Then on Monday he tweeted: "Can you imagine if the election results were the opposite and WE tried to play the Russia/CIA card. It would be called conspiracy theory!
"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?"
Why the Trump pushback? Anthony Zurcher, BBC News, Washington
Despite Donald Trump's boasts to the contrary, he's entering the White House with a very tenuous claim to a presidential mandate. He trails Democrat Hillary Clinton in the popular vote by 2.8 million votes, and while he posted a comfortable electoral college win, by historical standards it ranks towards the bottom of victory margins (46th out of 58 presidential contests).
This probably explains why the Trump team has been pushing back so vociferously against the allegations that Russian hackers interfered in US politics in an attempt to tilt the election to the Republican. Like the Green Party bid for recounts in three key swing states, it could be viewed as undermining the legitimacy of Mr Trump's victory.
Never mind that the recounts were extremely unlikely to appreciably change the election results or that Russian hacking is well down the list of factors that contributed to Mrs Clinton's defeat. Mr Trump's angry tweets, and the indignation expressed by his supporters, is evidence enough that the president-elect feels threatened - and is responding with sweeping denunciations of his critics.
In the case of the Russian story, however, concern over foreign meddling is bipartisan, so Mr Trump's recent diatribes may come at a high political price.
The FBI said in October that it believed Russia was behind the Democratic Party hacks, but on Friday the CIA went further by concluding Russia's motive was to help Mr Trump.
On Monday, the Hillary Clinton campaign, which lost to Mr Trump in last month's election, said it was supporting an effort by a handful of members of the electoral college to request an intelligence briefing on the latest hacking allegations.
The electoral college meets next week to ratify the results of the election.
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.
How to catch a hacker
While a company that is breached by hackers can really only work from the digital evidence left behind, nation states or intelligence agencies have many more sources to draw on when gathering evidence, said Rick Holland, vice-president of strategy at cyber-security firm Digital Shadows.
"They have a full spectrum of capabilities such as signal intelligence and human intelligence," he said, adding: "It's definitely not all cyber-based."
That extra evidence meant intelligence agencies could be more confident with their conclusions than many others, he said.
"It's certainly not simple," said Mr Holland. "But I do not think attribution is impossible when it comes to nation-states at all."
Mr Holland admitted that some nation states did sometimes run so-called "false flag" operations that attempted to pin the blame for an attack on someone else.
It could be difficult to unpick who was behind an attack because both spies and cyber-criminals used each other's attack tools and methods in a bid to throw investigators off the scent.
"There is a lot down that rabbit hole when it comes to nation states," he said.
While nation states did try to hide their attacks, there were times when knowing who was behind an attack was a useful diplomatic tool.
"Some nation states are very obvious and want you to know who was behind it," he said. "They will put you on notice that they did this."