US NATIONAL security adviser Michael Flynn has resigned after reports that he misled Vice President Mike Pence about contacts with a Russian diplomat.

The departure has disrupted President Donald Trump’s White House team less than a month after his inauguration.

In his resignation letter, Flynn, pictured, said he gave Pence and others “incomplete information” about his calls with Russia’s ambassador to the US. The Vice President, apparently relying on information from Flynn, initially said the national security adviser had not discussed sanctions with the Russian envoy, but Flynn later conceded the issue might have come up.

Such conversations would breach diplomatic protocol and possibly violate the Logan Act, a law aimed at keeping private citizens from conducting US diplomacy.

The Justice Department had warned the White House late last month that Flynn could be in a compromised position because of contradictions between his public depictions of the calls and what intelligence officials knew to be true based on routine recordings of communications with foreign officials in the US.

Kellyanne Conway, a close aide to Trump, said on Monday that Flynn continued to have the “full confidence” of the President. However, on Tuesday she said in televised interviews that the President had supported Flynn out of loyalty but the situation reached a “fever pitch” and had become “unsustainable”.

“By night’s end, Mike Flynn had decided it was best to resign. He knew he’d become a lightning rod, and he made that decision,” she told NBC’s Today show.

Asked why the White House did not move sooner after being warned by the Justice Department that Flynn was at risk of blackmail, she was vague. “As time wore on, obviously the situation became unsustainable,” she said. “We’re moving on.”

Trump named retired Lieutenant General Keith Kellogg as acting national security adviser. Kellogg was previously the National Security Council chief of staff, and advised Trump during the election campaign. Trump is also considering former CIA director David Petraeus and Vice Admiral Robert Harward, a US Navy SEAL, according to a senior administration official.

A US official said Flynn was in frequent contact with Russian ambassador Sergey Kislyak on the day the Obama administration imposed sanctions on Russia for election-related hacking, and at other times during the transition.

In other news, the Senate has confirmed Linda McMahon, the former chief of World Wrestling Entertainment (WWE) as the new boss of the Small Business Administration.

Senators voted 81-19 to appoint McMahon, who served as the chief executive of WWE before stepping down to run twice for the Senate in Connecticut. She lost both races despite spending $100 million (£80m).