The meeting attended by U.S. Defense Secretary Ash Carter and counterparts from NATO's other 27 countries was overshadowed by concerns about Russia's recent military actions in Syria. On Wednesday, Russian warships fired a volley of cruise missiles in the first combined air-and-ground assault with Syrian government troops since Moscow began its military campaign in the country last week.

U.S. officials said Thursday that some of those missiles missed their targets and landed in Iran.

Over the weekend, Turkey reported back-to-back violations of its airspace by Russian warplanes.

Stoltenberg said NATO had already increased "our capacity, our ability, our preparedness to deploy forces, including to the south, including in Turkey, if needed."

However, pressed about what NATO precisely intended to do to aid Turkey, which shares a border with Syria, Stoltenberg told a news conference the mere existence of a beefed-up alliance response force, as well as a new and highly nimble brigade-sized unit able to deploy within 48 hours, may suffice.

"We don't have to deploy the NATO Response Force or the spearhead force to deliver deterrence," Stoltenberg said. "The important thing is that any adversary of NATO will know that we are able to deploy."

Carter predicted Russia's support for the government of Syrian President Bashar Assad, including the new joint offensive, "will have consequences for Russia itself," adding: "I also expect that in coming days the Russians will begin to suffer casualties in Syria."

Echoing Winston Churchill's celebrated pronouncement in 1946 that an "iron curtain" had fallen across Soviet-dominated Eastern Europe, Carter told a news conference that modern-day Russia continues to "wrap itself in a shroud of isolation," and only the Kremlin can decide to alter that course.

Russia called its penetration of Turkey and NATO airspace a minor incident that was unintentional, but NATO issued a strongly worded statement insisting such violations must cease.

"We see an escalation of Russian military activity in Syria," Stoltenberg said. "And the ministers agreed that Russia's military escalation in Syria raises serious concerns."

He said NATO was "constantly assessing" the situation with Turkey's leaders, and that he would meet Thursday with Turkish Defense Minister Mehmet Vecdi Gonul.

Carter essentially accused the government of Russian President Vladimir Putin of lying about its actions and intentions in Syria, saying "what is clear is that Russia said one thing and did another."

As an example, the Obama administration official said, Moscow has insisted it is striking facilities of the Islamic State militant group, but that so far this hasn't matched up with the targets Russia is blasting from the air.

"They have initiated a joint ground offensive with the Syrian regime, shattering the facade that they're there to fight ISIL," Carter said, using an acronym for Islamic State.

German Defense Minister Ursula von der Leyen said Russia must recognize that if it targets opposition groups in Syria that are fighting Islamic State, "Russia will strengthen IS, and this can be neither in the Russian interest, nor in our interest."

British Defense Secretary Michael Fallon accused Russia of making a serious situation "much more dangerous." Many NATO officials, including Stoltenberg, have expressed fears there could be an encounter, accidental or otherwise, between Russian planes and the air forces of the U.S.-led coalition attacking Islamic State in Syria.

Carter said the Russians "shot cruise missiles from ships in the Caspian Sea without warning. They've come within just a few miles of one of our unmanned aerial vehicles."

Dutch Defense Minister Jeanine Hennis-Plasschaert said that in Syria, "Russia is not constructive, not reliable and not cooperative — so it is of great concern."

Thursday's meeting, the ministers' first since June, implemented further changes in the alliance, in line with a blueprint ordered by President Obama and other NATO leaders at the 2014 Wales summit, a reform process expected to last until the next summit in July 2016 in Warsaw.

A retooled NATO is supposed to be able to deal faster and more potently with an array of new security challenges, Putin's Russia and armed Islamic extremism in the Middle East and North Africa chief among them.

The new measures agreed upon Thursday include finalized plans, including command and control arrangements, for a NATO Response Force of up to 40,000 — twice the current size — and creation of new NATO headquarters offices in Hungary and Slovakia to enhance those Eastern European nations' defenses and speed reinforcement by their allies in the event of a real or perceived threat from Russia.

"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.

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