A top U.S. official is voicing concern that Moscow may be preparing to invade Ukraine.
For days, Western officials have been warning about the Russian military buildup along the border with Ukraine.
After a visit to U.S. European Command Headquarters, U.S. Defense Secretary Chuck Hagel made his concern clear.
“When you see the buildup of Russian troops and the sophistication of those troops, the training of those troops, the heavy military equipment that's being put along that border, of course it's a reality and it's a threat," Hagel said.
Hagel’s warning echoed earlier statements by Poland’s prime minister and by NATO, which says Russia now has about 20,000 troops massed along the border, following a significant increase in recent days.
At a news conference late Wednesday, U.S. President Barack Obama rejected - for now - calls to provide Ukraine with lethal military aid.
“If you start seeing an invasion by Russia, then that’s a different set of questions. We’re not there yet,” the president said.
Mr. Obama said instead that sanctions designed to hit hard at the Russian economy should be given more time to work.
“We’re doing exactly what we should be doing and we’re very pleased that our European allies and our partners joined us.”
Russian scholar David Satter of the Hudson Institute said whether sanctions will sway Russian President Vladimir Putin and his allies is not at all clear.
“They could be described accurately as a gang with a foreign policy. They don’t have any type of strategic vision beyond what’s necessary to keep themselves in power,” Satter said.
On a call Wednesday with German Chancellor Angela Merkel, the Russian president voiced concerns about the escalating humanitarian problems in eastern Ukraine - a statement met with suspicion by some Western officials who see it as a pretense for Russian military intervention.
Still, U.S. officials say what they find most worrisome are the capabilities of the Russian forces massed along Ukraine's border.
“What matters is that they continue to reinforce these units here, that they are very capable and very ready,” said Pentagon spokesman Rear Admiral John Kirby.
He warned Tuesday that Russia’s armor, artillery, air defense and special forces are all much closer to the border than they’ve been before.