The moves signal a major pivot for the Biden administration, which until recently was taking a restrained stance on Ukraine, out of fear of provoking Russia. But as President Vladimir V. Putin of Russia has ramped up his threatening actions toward Ukraine, and talks between American and Russian officials have failed to discourage him, the Biden administration is moving away from its previous strategy.
At the same time, the administration continues to insist that the United States has no intention of going to war with Russia over the issue. Since Ukraine is not in NATO, the alliance is not bound by its treaty to come to Ukraine’s defense. Russia’s massing of more than 100,000 troops on Ukraine’s border, and NATO’s response, has nonetheless raised the specter of a war that could escalate and widen.
“I don’t think anybody wants to see another war on the European continent,” Mr. Kirby said.
In a meeting on Saturday at Camp David, the presidential retreat in Maryland, senior Pentagon officials presented Mr. Biden with several options that would lead to a shift in U.S. military assets much closer to Russia’s doorstep, administration officials said.
The bulk of the troops being put on higher alert are active-duty ground troops, including combat brigades, medical, aviation, transportation, intelligence and surveillance forces with their equipment, Mr. Kirby told reporters. He declined to identify the specific units, saying that families were being notified on Monday.
“High alert” means the troops are now on what Defense Department officials characterized as a tighter leash, in case deployment orders come quickly. In some cases, officials said, units that have been prepared to deploy within 10 days must now be prepared to deploy within five days.