The outgoing Secretary of State, fired by President Trump via Twitter, failed to thank or praise his former boss in his outgoing address.
Sacked US Secretary of State Rex Tillerson left office warning about the dangers of Russia's behaviour on the world stage.
In his outgoing press conference, he said much work remained to respond to Moscow's "troubling behaviour and actions".
"Russia must assess carefully as to how its actions are in the best interests of the American people, and of the world more broadly. Continuing on their current trajectory is likely to lead to greater isolation on their part, a situation which is not in anyone's interest," he said.
Tillerson was fired by President Donald Trump via a tweet after just fourteen months in the job, and has been replaced by the CIA Director Mike Pompeo.
President Trump says they didn't agree on matters.
"Rex and I've been talking about this for a long time. We've got a long actually quite well but we disagreed on things. When you look at the Iran deal: I think it's terrible. I guess he thought it was OK. I wanted to either break it or do something. And he felt a little bit differently. So we were not really thinking the same," the president said.
In his final address, Rex Tillerson says he received a call three hours after the termination tweet. He thanked career diplomats, service members and the American people - but did not praise Trump or his policies.
"I close by thanking all for the privilege of serving beside you for the last 14 months. Importantly to the 300 plus million Americans: Thank you for your devotion to a free and open society, to acts of kindness towards one another, to honesty and the quiet hard work that you do every day to support this government with your tax dollars."
From Washington, Hans Nichols NBC News for euronews explains how key this decision is, "This does seem to come down to the President wanting HIS team in place for when these negotiations, potential direct talks between President Trump and Kim Jong Un start over the North Korean peninsula. We don't know where that would be but we do know that Mike Pompeo will play a crucial role in preparing President to those talks. Remplacing him at the CIA will be Gina Haspel, she will be controversial because of her role in early 2000s in potential "black sites" and torture. Now, what this means for foreign policy? You can say that it could potentially portend a more hawkish approach on North Korea."