Washington, US (BBN) – Donald Trump’s national security adviser, Michael Flynn, has resigned over his contacts with Russia, the White House has announced.
Flynn is alleged to have discussed US sanctions with the Russian ambassador before Trump took office, reports BBC.
He is said to have misled officials about the conversation.
Earlier, US media reported that the Justice Department had warned the White House about the contacts late last month.
They said that Flynn might be vulnerable to Russian blackmail.
Senior Democrats had called for Flynn to be fired.
It is illegal for private citizens to conduct US diplomacy, and the calls happened late last year before Flynn was appointed to the administration.
In his letter of resignation, Flynn said he had “inadvertently briefed the vice-president-elect and others with incomplete information regarding my phone calls with the Russian ambassador”.
A White House statement said Lt Gen Joseph Keith Kellogg had been appointed as interim replacement.
Flynn, a retired Army lieutenant general, initially denied having discussed sanctions with Ambassador Sergei Kislyak, and Vice-President Mike Pence publicly denied the allegations on his behalf.
However, Flynn later told the White House that sanctions may have been discussed.
Kremlin spokesman Dmitry Peskov told reporters on Monday that Flynn and Kislyak did not discuss lifting sanctions.
Democratic House Minority Leader Nancy Pelosi on Monday called for Trump to fire Flynn, tweeting that he “cannot be trusted to serve America’s best interests and national security instead of Russia’s”.
Several House Democrats have called on Oversight Committee Chairman Jason Chaffetz to launch an investigation into Flynn’s ties to Russia.
Republican Senator Susan Collins of Maine said it would also be “troubling” if Flynn had been negotiating with a foreign government before taking office.
Flynn, who was previously fired by Barack Obama as head of the Defense Intelligence Agency, was an ardent supporter of Trump during the campaign.
He became a close ally of both the president and his chief strategist, Steve Bannon.
He encouraged tougher policies on Iran and a softer policy on Russia, but questions were raised about his perceived closeness to Moscow.
 Flynn is known to have spoken with Russian ambassador Sergei Kislyak several times by phone in December;
 Flynn denied that he and Kislyak had discussed US sanctions and Vice-President Mike Pence also denied the claims on his behalf;
 A spokesman for Flynn then backtracked, telling reporters the adviser “couldn’t be certain” he had not discussed the sanctions;
 On Monday, White House counsellor Kellyanne Conway said Trump had “full confidence” in Flynn;
 White House spokesman Sean Spicer later said the president was “evaluating the situation”. Hours later, Flynn resigned.
Retired Lt Gen Joseph Keith Kellogg has been appointed acting national security adviser, and is far from a newcomer to the Trump team.
He brings more than 30 years’ experience in the army, and served in Vietnam, Cambodia, Panama and the Gulf.
During the Iraq war, he helped manage the coalition authority running the country in 2003 and 2004, before working for a defence contractor, according to Bloomberg.
More recently, he advised Trump on national security issues during his campaign, and went on to be appointed chief of staff in the new administration’s National Security Council.