Donald Trump. AP President-elect Donald Trump mocked US intelligence officials on Tuesday in a tweet claiming his briefing on Russian cyberattacks was delayed, and he once again cast doubt on their claims that Russia interfered with the presidential election.

"The 'Intelligence' briefing on so-called 'Russian hacking' was delayed until Friday, perhaps more time needed to build a case. Very strange!" Trump said on Twitter.

A senior US intelligence official immediately countered Trump's claim, however, NBC News reported, saying the briefing with the heads of the NSA, the CIA, the DNI, and the FBI was "always" scheduled for Friday.

Trump doubled down on his apparent doubts on Russia's involvement Wednesday morning, citing WikiLeaks founder Julian Assange's interview with Fox News that aired Tuesday.

Speaking with Fox News host Sean Hannity, Assange denied that Russia provided WikiLeaks with the leaked Democratic emails it released during the 2016 campaign.

Last week, Trump said he agreed to meet with intelligence officials about Russia's involvement in the hacks, though he added it was "time to move on."

He also claimed he would reveal insider information about the cyberattacks on Tuesday or Wednesday of this week, though a member of Trump's team told CNN that Trump would not be following through.

Lawmakers slammed Trump's Tuesday-night tweet.

"Really wish we saw more PEOTUS respect for our intelligence professionals," Sen. Mark Warner of Virginia said on Twitter. "Proves the need for Congress to give the American people a timely bipartisan probe."

The incoming Senate minority leader, Chuck Schumer, also weighed in, calling Trump's comments "really dumb" during an interview with MSNBC's Rachel Maddow.

"Let me tell you, you take on the intelligence community, they have six ways from Sunday at getting back at you," Schumer continued.

The FBI, the CIA, and the Director of National Intelligence concluded in December that Russia interfered with the election in part to help Trump secure the presidency, with Russian President Vladimir Putin possibly being personally involved.

As punishment, President Barack Obama announced last week a new round of sanctions against Russia, including the removal of 35 intelligence Russian officials from the US. Trump has consistently questioned the allegations against Russia.

Tuesday's tweet was another example of Trump's dismissive attitude toward the intelligence agencies he'll soon be working with. Last month, the president-elect brushed off concerns he wasn't attending his traditional daily intelligence and national security briefings.

"I get it when I need it," Trump said.

"I'm, like, a smart person," he added. "I don't have to be told the same thing in the same words every single day for the next eight years. I don't need that. But I do say, 'If something should change, let us know.'"

Peter Jacobs contributed to this report.