President Donald Trump’s national security advisor Michael Flynn has resigned after he came under fire over his contacts with Russian officials.

The resignation comes after the Justice Department announced that officials had “warned the Trump administration last month that Flynn misled administration officials regarding his communications with the Russian ambassador to the United States and was potentially vulnerable to blackmail by the Russians.”

Flynn wrote an extensive resignation letter:

In the course of my duties as the incoming National Security Advisor, I held numerous phone calls with foreign counterparts, ministers, and ambassadors. These calls were to facilitate a smooth transition and begin to build the necessary relationships between the President, his advisors and foreign leaders. Such calls are standard practice in any transition of this magnitude.

Unfortunately, because of the fast pace of events, I inadvertently briefed the Vice President Elect and others with incomplete information regarding my phone calls with the Russian Ambassador. I have sincerely apologized to the President and the Vice President, and they have accepted my apology.

Reports emerged earlier this morning that Flynn misled Vice President Mike Pence and others about talks he had with the Russian Ambassador Sergey Kislyak about sanctions former President Barack Obama passed against Russia due to interference with our election.

Pence went on Sunday talk shows to defend Flynn and insisted the advisor never spoke with the ambassador about the sanctions:

“General Flynn has been in touch with diplomatic leaders, security leaders in some 30 countries,” he said. “That’s exactly what the incoming national security adviser should do.”

“But what I can confirm, having spoken to him about it, is that those conversations that happened to occur around the time that the United States took action to expel diplomats had nothing whatsoever to do with those sanctions.”