President Donald Trump with Chief of Staff Reince Priebus, Vice President Mike Pence, senior adviser Steve Bannon, communications director Sean Spicer, and Michael Flynn. REUTERS/Jonathan Ernst

Leon Panetta isn't mincing words following the resignation of President Donald Trump's national security adviser over contacts with Russian officials.

"I've never been so nervous in my lifetime about what may or may not happen in Washington," Panetta, who served as President Barack Obama's defense secretary from 2011 to 2013, said in a Tuesday interview with The New York Times.

Panetta, a Democrat, has served nine presidents - Democrat and Republican - in various high-profile positions, including as chief of staff, CIA director, and secretary of defense in a career spanning decades.

"I don't know whether this White House is capable of responding in a thoughtful or careful way should a crisis erupt," Panetta told The Times. "You can do hit-and-miss stuff over a period of time. But at some point, I don't give a damn what your particular sense of change is all about, you cannot afford to have change become chaos."

Former US Secretary of Defense Leon Panetta discussing his book "Worthy Fights" at George Washington University in Washington in 2014. REUTERS/Jonathan Ernst

Panetta's comments came a day after Michael Flynn resigned as national security adviser after it was revealed that he misled Vice President Mike Pence about the contents of a December phone call with Russia's ambassador to the US, Sergey Kislyak.

Flynn reportedly discussed the Obama administration's sanctions on Russia with Kislyak during the call, giving the impression that the sanctions would be "revisited" at a later time.

Sally Yates, the acting attorney general at the time, in January informed the White House that Flynn's conversation with Kislyak was "potentially illegal," though Trump took no immediate action. Yates was fired January 30 after refusing to enforce the Trump administration's temporary travel ban on people from seven majority-Muslim countries.

The Trump campaign also had repeated contact with Russian officials before the general election in November, The Times reported on Tuesday evening, citing US intelligence sources.

The head of US Special Operations Command, Gen. Raymond Thomas, echoed Panetta's sentiments, telling a military conference on Tuesday that the government was in "unbelievable turmoil."

"I hope they sort it out soon because we're a nation at war," Thomas said.

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