NATO Secretary-General Jens Stoltenberg says the alliance has renewed assurances to defend "all allies against any threat," amid new tensions with Russia over its aerial campaign in Syria.
Stoltenberg said NATO defense ministers meeting on October 8 gave the green light to a NATO Response Force of up to 40,000, twice the current size.
"All of this sends a clear message to all NATO citizens. NATO will defend you, NATO is on the ground, NATO is ready," Stoltenberg said.
In earlier remarks, Stoltenberg warned of a "troubling escalation" of Russian military activity in Syria, and said the alliance was prepared to deploy forces to NATO member Turkey if necessary after airspace violations by Russian warplanes.
Stoltenberg also urged Moscow to stop backing Syrian President Bashar al-Assad, describing such a position as "unhelpful."
Damascus and activists claim Russian strikes have facilitated expanded military operation by government troops to recapture territories from insurgents.
Based on reporting by AP and dpa