The possibility of an unrestrained escalation of the situation around Ukraine will lead to disastrous consequences, former CIA chief David Petraeus told CNBC.

"I think it is legitimate for U.S. leadership and for leadership of other countries to avoid starting World War III, as the phrase has been termed," he said.

Petraeus said Western policymakers should signal their moves adequately and refrain from going too far in offensive military action against Russia.

"Remember, in the beginning, there were these calls for no-fly zones over Ukraine, which I thought was just not fully thought through," he said.  "Because when you put U.S. aircraft into that airspace, and Russian aircraft … you can’t fly our aircraft without taking down the air defenses that could shoot them down. And now you’re into a U.S.-Russia war. And again, I think it’s understandable that U.S. leadership and that of other countries should have concerns about a spiraling beyond — as horrific as this is — a spiraling beyond where we are right now in the war in Ukraine."

Speaking of the possibility of a nuclear strike by Russia and possible U.S. retaliation, the former CIA chief said, it's about the situation just somehow getting out of hand. "Which is why it’s so important that as our national security advisor in the U.S., Jake Sullivan, has publicly stated, it’s very important that we have communicated in advance to the Russians, ‘if you do this, you can expect something along the lines of this’ — noting that obviously, there will always be a range of options presented to the president. And it depends specifically on you know, what happened, all this, that would determine what a response would be."

Ultimately, Petraeus believes, Putin is not suicidal.