Rejecting charges they are engaging in a Cold War-style arms race with Moscow, the U.S. and its NATO allies approved an array of military upgrades Wednesday that should help them come to the aid of a threatened alliance member faster, with better equipment and more firepower.

"We stand united in the way we are addressing the challenges we face," NATO Secretary-General Jens Stoltenberg said.

Meeting at NATO headquarters in Brussels, U.S. Defense Secretary Ash Carter and counterparts from Canada and NATO's European member nations ordered an increase in the strength of the alliance's Response Force, which was 13,000 at the start of 2015, to as many as 40,000.

Also, they added air, sea and special forces units to the force, which includes a highly mobile, multinational "spearhead" brigade of 5,000 ground troops the ministers ordered to be formed in February so NATO can reinforce any alliance member under threat within 48 hours.

Ministers also made it easier and quicker for NATO generals and civilian officials to mobilize the force and bring it into action, Stoltenberg told a news conference. He said NATO will also develop more detailed advance plans to use in the case of crisis, and that a new logistics headquarters will be opened to help NATO forces deploy faster.

Stoltenberg said the alliance revamp was in large part caused by Russia's annexation of Crimea from Ukraine, its alleged and continuing military incursion in eastern Ukraine, its ability to speedily mobilize large numbers of troops and its escalating rhetoric about use of nuclear weapons. But the NATO chief said the alliance's sole goal is to protect itself — not to threaten Moscow.

"We don't seek a new arms race," Stoltenberg said. "But we have to keep our nations safe. And we have to adapt when the world is changing."

Russia too has been growing its military capacities and last week, said it will add over 40 new intercontinental ballistic missiles this year alone. In early December, it flexed its muscle by airlifting state-of-the art Iskander missiles, which can be fitted with nuclear or conventional warheads, to its westernmost Baltic territory of Kaliningrad.

They were later pulled back, but the deployment clearly served as a demonstration of the Russian military's readiness to quickly raise the ante in a crisis.

On Tuesday, Carter announced during a visit to Estonia that the U.S. will spread about 250 tanks, armored vehicles and other military equipment across a half-dozen of NATO's easternmost members that feel most at risk from Russia.

Earlier, the U.S. defense secretary told reporters traveling with him that the Obama administration still hopes to work with the Russians on important issues like the Iran nuclear talks, the fight against Islamic State group and efforts to bring about peaceful regime change in Syria. But Carter said NATO must adapt its deterrence and response capabilities "in anticipation that Russia might not change under Vladimir Putin, or even thereafter."

Last September, the U.S. announced a plan to spend up to $1 billion on various actions to reassure European NATO members. The funds are paying for increased U.S. troop rotations, more exercises, more prepositioning of military equipment and upgrading of infrastructure.

Since possessing an ultra-fast reaction force is pointless if NATO's 28 member countries can't quickly agree in an emergency on how to use it, the alliance also decided on internal changes to "speed up political and military decision-making," Stoltenberg said.

Ministers granted U.S. Air Force Gen. Philip Breedlove, the alliance's supreme commander in Europe, greater authority to mobilize troops and get them ready to go. But Stoltenberg stressed that in the event of deployment, member countries' "full political control" over alliance actions, one of NATO's guiding principles, would be maintained.

Douglas Lute, U.S. ambassador to NATO, said Breedlove will have more latitude than at present to alert and assemble the reaction force. The power to decide on its use will remain with representatives of the governments of NATO's member countries, but the old step-by-step political decision-making sequence used to approve military operations will be simplified and compressed.

"So it's two parts: delegate some (powers) to Phil, and streamline those that remain at the political level," Lute said.

The latest changes at NATO follow broad policy decisions taken by President Barack Obama and other alliance leaders at the summit in Wales last September, and come at about the midway point between that meeting and the next NATO summit scheduled for July 2016 in Warsaw, Poland.

"Things over the last several years have gone at a dizzying pace, you might say," U.S. Air Force Secretary Deborah Lee James said during a visit this month to Brussels. "There has been more change than I can remember ever in a single two-year period, at least in the 34 years that I have been an observer on the defense scene."

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Associated Press writer Lolita Baldor in Brussels contributed to this report.