Nato has renewed assurances to defend allies in view of the ‘escalation of Russian military activities’ in Syria, the alliance's secretary-general says.
Jens Stoltenberg said defence ministers had decided to boost response forces to be able to deploy troops speedily.
Nato member Turkey has complained that Russian jets have violated its airspace recently.
Russia has used cruise missiles as well as air strikes in Syria. The Nato chief said Moscow's position was "unhelpful".
Announcing the doubling of the size of the Nato Response Force to 40k, Mr Stoltenberg said: "All of this sends a clear message to all Nato citizens. Nato will defend you, Nato is on the ground, Nato is ready."
He also urged Moscow to stop backing Syrian President Bashar al-Assad.