NATO'S chief told The Associated Press Thursday that failure is simply not an option in meeting the myriad threats that now menace the U.S.-led alliance.

"It's not only not an option, it's also something which will not happen," Jens Stoltenberg said on the eve of a landmark NATO summit. "Because we have proven during almost 70 years that we are able to deliver the necessary defense and deterrence, not to provoke a conflict, but to prevent a conflict."

Starting Friday, President Barack Obama and leaders of the 27 others NATO countries will take decisions in Warsaw on how to deal with a resurgent Russia, violent extremist organizations like Islamic State, attacks in cyberspace and other menaces to allies' security.

Many observers are calling it NATO's most crucial meeting since the 1989 fall of the Berlin Wall.

"We will succeed," Stoltenberg, the alliance secretary-general, said in an interview. "And the reason why I am so confident is that is that we have seen that the alliance has been able to adapt and to implement the biggest reinforcement of collective defense since the end of the Cold War."

Among the decisions expected from NATO leaders is ordering deployment of four multinational battalions to Poland and the Baltic states of Estonia, Latvia and Lithuania to act as a deterrent to Russia. But Stoltenberg said the alliance also wants to send the Kremlin "a very clear message that we don't want a new Cold War, we don't seek confrontation."

"The Cold War is history and it should remain so," Stoltenberg said. "And this idea, or this message, of defense and dialogue is a message that unifies the alliance. And since we are unified, we are also able to implement and to deliver on our decisions."