NATO Secretary General Jens Stoltenberg says there has been a "troubling escalation" in Russian military activity in Syria, after Moscow dramatically expanded its air campaign.
"In Syria, we have seen a troubling escalation of Russian military activities. We will assess the latest developments and their implications for the security of the alliance," Stoltenberg said as he went into a NATO defence ministers meeting dominated by the Syrian crisis.
"This is particularly relevant in view of the recent violations of NATO's airspace by Russian aircraft."
Russia launched its air campaign against what it terms "terrorist" targets in Syria last week but in the process, it has infringed on key NATO ally Turkey's airspace, prompting strong protests from the US-led alliance and Ankara.
On Wednesday (local time), Moscow upped the ante dramatically with the launch of an unprecedented series of cruise missile attacks to cover a Syrian army ground offensive against rebels seeking the ouster of long-term Russian ally President Bashar al-Assad.
NATO has stationed anti-missile Patriot batteries in Turkey to protect it from any spillover of the Syrian conflict but they are due to be removed later this year.
Asked if NATO would consider extending their mission in light of the Russian missile attacks, Stoltenberg said: "NATO is able and ready to defend all of the allies, including Turkey."
He cited measures taken to boost NATO's readiness, driven initially by Russia's intervention in support of pro-Moscow Ukraine rebels, and the creation of a very rapid response force which should be operational from next year.
This "spearhead" force, of about 13,000 troops, could be deployed both to the east and to the south if need be, he said.
"We are facing many challenges from many different directions. Conflict, instability and insecurity," he said.
"We are implementing the biggest reinforcement of our collective defence since the end of the Cold War."
On Wednesday Russian President Vladimir Putin said Moscow was synchronising its strikes with the Syrian army's ground movements against rebels.
Putin said Russian warships fired cruise missiles on Islamic State group positions in Syria for the first time.
A video map released by Russia's defence ministry showed the missiles launched from warships in the southern Caspian Sea and flying close to 1,500km through Iranian and Iraqi airspace before hitting targets in Syria.
A Syrian military source told AFP government troops had begun a broad ground operation near the village of Latmeen in Hama province, aided by Russian air cover.
The Syrian Observatory for Human Rights reported at least 40 Russian air strikes in Hama and neighbouring Idlib province, which is controlled by the powerful Army of Conquest alliance that includes Al-Qaeda affiliate Al-Nusra Front.