US National Security Adviser, Michael Flynn, has resigned over allegations that he discussed US sanctions with Russia before Donald Trump became President. Michael Flynn is said to have misled officials about his call with Moscow's ambassador before his own appointment.

It is not legal for private citizens to conduct US diplomacy. Flynn declared that he had inadvertently briefed the vice-president-elect and other people with incomplete information regarding my phone calls with the Russian ambassador.

The White House has named Lt Gen Joseph Keith Kellogg as his interim replacement. Mr Flynn initially denied having discussed sanctions with Ambassador Sergei Kislyak, Flynn will have serious problems if he had that type of conversation.

More details emerged, violation of the Logan Act

Flynn came under further pressure on Monday when details of his phone call emerged and the justice department had warned the White House about him misleading senior officials. According to the Washington Post, the message was delivered by then-Acting Attorney General Sally Yates, who was subsequently dismissed by President Trump for opposing his travel ban.

US officials had told the New York Times and Washington Post that Flynn explicitly talked about the sanctions and hinted that President Trump might be willing to lift them. According to Flynn, he never discussed about sanctions in his call with Kislyak. That kind of conversation could be a violation of a federal law, the Logan Act, which bans people outside the executive branch from making foreign policy on behalf of the US administration.

No one has ever been prosecuted under the Logan Act, but Michael Flynn is facing a second and potentially more dangerous investigation. The FBI is probing his interactions with Kislyak, and resigning from his government post won't protect Flynn from potential future criminal prosecution.