The resignation comes amid reports that US security agencies had taken to withholding sensitive intelligence from their presidential briefings, because this White House is not to be trusted with the nation's secrets.
In a resignation letter, Flynn said he held numerous calls with the Russian ambassador to the U.S. during the transition and gave "incomplete information" about those discussions to Vice President Mike Pence. The vice president, apparently relying on information from Flynn, initially said the national security advisor had not discussed sanctions with the Russian envoy, though Flynn later conceded the issue may have come up.
Trump named retired Lieutenant General Keith Kellogg as the acting national security advisor. Kellogg had previously been appointed the National Security Council chief of staff and advised Trump on national security issues during the campaign.
The Justice Department warned the Trump administration weeks ago that contradictions between the public depictions and the actual details of the calls could leave Flynn in a compromised position, an administration official and two other people with knowledge of the situation told The Associated Press Monday night.
One person with knowledge of the situation said the Justice Department alerted the White House that there was a discrepancy between what officials were saying publicly about the contacts and the facts of what had occurred. Pence - apparently relying on information from Flynn - initially said sanctions were not discussed in the calls, though Flynn has now told White House officials that the topic may have come up.
Acting US attorney general Sally Q Yates informed the Trump White House that she believed Michael Flynn had misled senior administration officials about the nature of his communications with the Russian ambassador to the United States.
She warned that the national security advisor was potentially vulnerable to Russian blackmail, current and former US officials said.
Flynn's departure less than one month into the Trump administration marks an extraordinarily early shakeup in the president's senior team of advisors. Flynn was a loyal Trump supporter throughout the campaign, but his ties to Russia caused concern among other senior aides.
Flynn initially told Trump advisors that he did not discuss sanctions with the Russian envoy during the transition. Vice President Mike Pence, apparently relying on information from Flynn, publicly vouched for the national security advisor.
Flynn later told White House officials that he may have discussed sanctions with the ambassador.
Photo: National security adviser General Michael Flynn.