Congress' top Republicans on Monday endorsed investigations into the CIA's belief that Russia meddled in last month's election to help Donald Trump win, putting top Republicans on a collision course with the incoming president.

The president-elect has dismissed the intelligence reports as "ridiculous" defying an increasing number of senators from his own party, as well as top Democrats, the Central Intelligence Agency and the outgoing White House.

"The Russians are not our friends," declared Senate Majority Leader Mitch McConnell as Republican leaders steered toward a path sharply at odds with the president-elect's belittling dismissal of the spy agency's assessment and his past praise for Russian President Vladimir Putin.

McConnell expressed support for probes by the senate's intelligence panel, as well as the Armed Services Committee (ASC).

McConnell stopped short of saying whether he believes Russia tried tilting the election toward Trump, but seemed to warn the incoming president and his staff against having too cozy a relationship with the Kremlin.

"I hope that those who are going to be in positions of responsibility in the new administration share my view" about Moscow.

Republican Senator John McCain, who chairs the ASC, told CBS television that there was "no doubt" about the hacking.

"It's another form of warfare and the entire issue is going to be examined by the Armed Services Committee because it's a threat to our national security," he said.

But Trump remained dismissive of the intelligence reports, and took to Twitter to voice his displeasure:

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 the election?

Recounts closed in key states

Trump's dismissal comes as electoral recounts in three swing states have been closed without any change to the final outcome. A 10-day review in Wisconsin - carried out due to concerns of irregularities in results stemming from electronic voting machines - came to an end, with the results showing a slight gain for Trump.

The president-elect, who previously denigrated the recount effort, took to Twitter again to slam the effort at ensuring electoral transparency, this time labelling it a 'scam.'

In Pennsylvania a federal judge rejected a recount request by Green Party candidate Jill Stein, who suggested that the abnormalities may have resulted from a hack of electronic voting machines.

In a 31-page opinion, however, US District Judge Paul Diamond in Philadelphia said it "borders on the irrational" to suspect hacking occurred in Pennsylvania.

And in Michigan, the state's top court denied Stein's last-ditch appeal on Friday to keep a recount going.

bik/kl (AP, AFP)