NATO Secretary General Jens Stoltenberg on Thursday warned of a "troubling escalation" in Russian military activity in Syria, as defense ministers held talks on Moscow's dramatically expanded air campaign.
Stoltenberg also said the North Atlantic Treaty Organization was ready to deploy forces in key member Turkey if needed after Ankara complained about a series of airspace violations by Russian planes.
"In Syria, we have seen a troubling escalation of Russian military activities," Stoltenberg told reporters as he went into a NATO defense ministers meeting dominated by the Syrian crisis, according to the AFP news agency.
"We will assess the latest developments and their implications for the security of the alliance," the former Norwegian prime minister said.
"This is particularly relevant in view of the recent violations of NATO's airspace by Russian aircraft," he added.
Russia conducted its first airstrikes in Syria last week, and on Wednesday Moscow ramped up its war by unleashing cruise missiles from the Caspian Sea.
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 now consider extending their mission in light of Russia's actions, Stoltenberg said, "NATO is ready and able ready to defend all allies against any threat, including Turkey."
Stoltenberg cautioned that the situation demanded more than ever a political solution and urged Russia to play a "constructive" role by not targetting the rebels in support of Assad.
"What we see is that there is a renewed need for political initiatives ... because in the long term there is no military solution," he said, according to AFP.
While Russia has been claiming it is targeting Islamic State (ISIS), the U.S. State Department said Wednesday that most of Russia's barrage of airstrikes in Syria are not hitting ISIS terrorists as it claims.
In the first Russian strikes against the Homs and Hama districts of the country, an unnamed American official later said the targets were "moderate" rebel groups fighting ISIS.