AP – NATO reinforced its defenses against Russia from the Baltic to the Black Sea, delivering what NATO's chief called a clear message to Moscow that "if any of our allies is attacked the whole alliance will respond as one."

Jens Stoltenberg, the alliance secretary-general, told a news conference that NATO defense ministers agreed to deploy four multinational battalions on a rotational basis to Estonia, Latvia, Lithuania and Poland.

He said the ministers also agreed on "tailored measures" to enhance "defense and deterrence" in the Black Sea region, including the advance stockpiling of equipment and supplies.

"NATO is an alliance that delivers," Stoltenberg said.

Earlier, as the defense ministers began the first of two days of meetings at NATO headquarters, the secretary-general called "defending our territory and protecting our people" NATO's primary task.

The ministers' meetings are meant to set the stage for NATO's summit next month from July 8-9 in Warsaw. On Tuesday and Wednesday, ministers are also expected to agree to cooperate more closely with the European Union in security affairs, discuss how to improve NATO cyberdefense, intelligence-sharing and decision-making to face current challenges, and meet with Ukraine's defense minister.

Without disclosing details, Stoltenberg also said "we will establish a framework to deal with threats and challenges from the south" - NATO speak for the Islamic extremist violence that has become widespread in the Middle East and North Africa.

The U.S., Britain and Germany have already committed to spearheading the development of three of the four battalions earmarked for Poland, Estonia, Latvia and Lithuania. A senior U.S. official said Canadian leaders are currently meeting to discuss the possibility that they would coordinate the development of the fourth battalion.

Canadian defense spokeswoman Ashley Lemire said that, "Unfortunately, we are not in a position to provide any additional details at this time. As a committed NATO ally, Canada is actively considering options to effectively contribute to NATO's strengthened defense and deterrence posture."

U.S. officials said it's not yet clear whether the Pentagon will use troops currently in Europe to form its battalion or bring in others. U.S. Defense Secretary Ash Carter told reporters Monday that the U.S. may well contribute most or all of the 800-1,000 troops needed for the unit.

British Defense Secretary Michael Fallon told reporters that in early 2017 Britain will deploy one of the "framework battalions."

"That's around 500 British personnel rotating on a continuous basis," Fallon said. He said other countries will contribute to the multinational unit, including France, which will chip in a company.

Additionally, he said, Britain will send a company of between 150 and 200 troops, plus vehicles and equipment, to train and operate alongside Polish soldiers.

Fallon called the British actions "a very clear message that we are committed to defend the eastern flank. NATO is strong and united. ...We are ready to respond to any threat."

Stoltenberg said defense ministers also discussed establishing a Romanian-led multinational "framework brigade" of ground troops to help defend the Black Sea area. In a statement, NATO deputy spokeswoman Carmen Romero said that the proposed unit, with a Romanian headquarters and a Romanian and Bulgarian battalion, would serve as a framework for training and exercises with other NATO member countries' militaries. The brigade's strength was expected to be roughly 3,000-5,000.

NATO's latest actions, said one senior U.S. defense official, are key to putting some teeth behind talks with Russia, which have centered on concerns about Moscow's military actions in Crimea and eastern Ukraine. NATO officials also predicted support for a Romanian proposal for a joint training initiative that focuses on specific operational requirements of the southeastern European region and promotes interoperability of NATO forces through training and exercises.

Additional proposals are under consideration to increase air and naval defenses in the Black Sea, where a Russian naval fleet based at Sevastopol in Crimea is a major concern, NATO officials say.

Speaking to reporters before ministers met, Stoltenberg said that even as NATO reacts to what it sees as a potent security threat from a newly resurgent and unfriendly Moscow, "at the same time we convey a very strong message that we don't seek a confrontation with Russia. We don't want the new Cold War."

He said it "is important that we continue to keep channels for political dialogue open, but also military contacts."

During their talks in Brussels, U.S. Defense Secretary Ash Carter and his counterparts from Canada and NATO's European members are also expected to consider providing AWACS surveillance planes to support the U.S.-led coalition fighting ISIS in Iraq and Syria, discuss how to support countries in the Middle East and North Africa threatened by extremist violence and assess what NATO can do to assist an EU operation attempting to stop people trafficking in the Mediterranean.