"At the same time, we need to make sure that there is no misunderstanding about our commitment to defend and protect all Allies.", APA reports citing CNN.
He said that NATO forces have increased their "defensive presence" in the eastern part of the Alliance.
Stoltenberg also called on the US, Europe and Canada for support.
"I welcome the strong commitment from the United States with more troops," he said.
"I met many of them. And it is always great to meet US troops in Europe and to see their commitment, and their professionalism, being part of the transatlantic bond.
"I also welcome that European Allies and Canada are stepping up with more presence in the eastern part of the Alliance, on land, at sea and in the air.
"If anything, I think the crisis we are faced with now demonstrates the importance of North America standing together in strategic solidarity in NATO," he added.
Russian forces have occupied Ukraine's Zaporizhzhia nuclear power plant following a fire at the facility early on Friday, Ukrainian authorities have said.
The fire was extinguished in the early hours of Friday morning.