President-elect Donald Trump at a rally in Grand Rapids, Michigan, on Friday. REUTERS/Mike Segar President-elect Donald Trump continued to express skepticism on Monday about whether Russian hackers interfered in the US election, insisting that if Republicans had made that accusation, it would be treated as a "conspiracy theory."

"Can you imagine if the election results were the opposite and WE tried to play the Russia/CIA card," Trump tweeted. "It would be called conspiracy theory!"

He continued: "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?"

The Director of National Intelligence and the Department of Homeland Security had said one month before the election, however, that officials were "confident" the Russian government directed hacks on US political institutions.

Internal emails from members of the Democratic National Committee and John Podesta, the chairman of Hillary Clinton's campaign, were leaked online throughout the campaign.

The Washington Post and The New York Times reported on Friday that an assessment by the CIA concluded that Russia interfered in the election to help Trump's presidential bid.

Trump has been reluctant to pin blame for the hacks on Russia. In an interview that aired on "Fox News Sunday," he called the claim "ridiculous" and "just another excuse" for Clinton's surprise loss last month.