WASHINGTON:President Donald Trump on Tuesday fired top U.S. cybersecurity official Chris Krebs in a tweet, accusing him without evidence of making a "highly inaccurate" statement affirming the security of the Nov. 3 election.

Trump has made unsubstantiated claims of widespread voter fraud and refused to concede defeat to President-elect Joe Biden. His campaign has filed a flurry of lawsuits in battleground states, although election officials in both parties have said they see no evidence of serious irregularities.

Reuters reported last week that Krebs, who worked on protecting the election from hackers but drew the ire of the Trump White House over efforts to debunk disinformation, had told associates he expected to be fired.

Trump said on Twitter on Tuesday that Krebs had assured people that the election had been secure when there were "massive improprieties and fraud--including dead people voting, Poll Watchers not allowed into polling locations," and voting machine errors that flipped votes from Trump to Biden.

Twitter slapped warning labels on Trump's tweets, noting: "This claim about election fraud is disputed."

Krebs headed up the Department of Homeland Security's Cybersecurity and Infrastructure Security Agency from its inception two years ago.

He angered the White House over a website run by CISA dubbed "Rumor Control," which debunks misinformation about the election, according to the three people familiar with the matter.

A CISA representative did not respond to a request for comment.

The Reuters report last week prompted an outpouring of support from security experts across the country, who praised Krebs for his bipartisan work in the past two years.

'HONORED TO SERVE'

On his own Twitter account, Krebs did not back down, writing: "Honored to serve. We did it right. Defend Today, Secure Tomorrow."

Like others who have run afoul of Trump, Krebs learned of his dismissal when he saw the tweet, a person close to him said.

White House officials previously complained about CISA content that pushed back against numerous false claims about the election, including that Democrats were behind a mass election fraud scheme. CISA officials declined to delete accurate information.

Among other things, one Krebs associate said the White House was angry about a post rejecting a conspiracy theory that falsely claimed an intelligence agency supercomputer and program, purportedly named Hammer and Scorecard, could have flipped votes nationally. No such system exists, according to Krebs, election security experts and former U.S. officials.

The Biden campaign did not immediately respond to a request for comment. But Trump's move was quickly slammed by security officials and White House critics.

"Krebs was doing important work defending critical infrastructure and fighting disinformation," said Harri Hursti, a leading critic of voting machine security. "His firing is very disappointing and appears to be an attempt to undermine the great work he and others at DHS/CISA have been doing."

Democrat Adam Schiff, who heads the House of Representatives Intelligence Committee, said: “Throughout this election, the CISA and Director Krebs have worked diligently to safeguard our elections, provide vital support to state and local election officials, and inform the American people about what was true and what was not."

Independent Senator Angus King said Trump was “firing Mr. Krebs for simply doing his job."

"I hope that President-elect Biden will recognize Chris’s contributions, and consult with him as the Biden administration charts the future of this critically important agency,” King said.