President-elect Donald Trump tweeted he thought it was "very strange" his intelligence briefing on the Russian hacking had been delayed. He's pictured here with Omarosa Manigault in Detroit, Sept. 3, 2016. Carlo Allegri/Reuters

President-elect Donald Trump, who has voiced skepticism on whether Russia was behind the hacking of Democrats’ email accounts and state voter databases to help him get elected, took a swipe at intelligence officials on Twitter Tuesday, complaining his briefing on the issue had been delayed.

Trump sarcastically accused intelligence officials of needing more time “to build a case” and tweeted he thought the delay “very strange.”

Last month, Trump tweeted it was impossible to figure out who was responsible for a hack unless the perpetrators are caught in the act.

And during the presidential debates, Trump said it was just as likely the hack was committed by some 400-pound man sitting on his bed.

State Department spokesman John Kirby earlier Tuesday told CNN the administration is “100 percent certain” Russia was involved in election-related hacking.

“There is no question,” Kirby said, that the Russians were attempting to undermine the election.

"And that's not just an assessment by the president or by Secretary [John] Kerry or other Cabinet officials. It's an assessment by the entire intelligence community," he said, rejecting Trump’s comments.

"The information is there, and it's rock solid. And we obviously would not have pursued the measures that we pursued without that level of certainty," he said. "So, yes, we are a 100 percent certain."

Julian Assange, the founder of WikiLeaks, which published the hacked emails, told Fox News Russia was not behind the hacked emails from the Democratic National Committee or Clinton campaign chairman John Podesta.

“We can say, we have said, repeatedly over the last two months that our source is not the Russian government and it is not a state party,” he said.

President Barack Obama last week ordered retaliation against Russia for the hacking.

“All Americans should be alarmed by Russia’s actions. In October, my administration publicized our assessment that Russia took actions intended to interfere with the U.S. election process,” he said in a statement. “These data theft and disclosure activities could only have been directed by the highest levels of the Russian government.”

Nine entities and individuals were sanctioned, two Russians were cited for using “cyber-enabled means to cause misappropriation of funds and personal information,” two Russian compounds were ordered closed and 35 diplomats were kicked out of the United States.