"We have to keep our security commitments to each other," said Assistant Secretary Victoria Nuland, adding that all NATO allies must contribute to the new "spearhead force which will allow us to speed forces to troubled spots."
NATO allies must stay the course in Ukraine, the top US diplomat for Europe insisted Tuesday, calling for alliance command and control centers to be set up quickly in Kiev's neighbors.
"And we must install command and control centers in all six frontline states as soon as possible," she said.
"NATO is a defensive alliance. Our goal is deterrence of aggression but if that fails we have to be ready," Nuland stressed in an address to the Washington-based Brookings Institution think tank.
With the death toll climbing in Ukraine's separatist east and the Russian-backed rebels refusing to return to the negotiating table, Nuland told the audience "Ukraine's frontline for freedom is ours as well."
"All allies must now contribute as much as they can to the effort and all must keep their .. defense spending pledges."
"Some governments are already trying to slink off the hook," she warned, without pointing the finger at any specific country.
On the issue of the biting sanctions imposed on Moscow by the United States and EU in tandem, Nuland insisted they were not aimed at punishing the Russian people but at forcing a change of policy by Russian President Vladimir Putin.
"Just a few weeks ago around tables in Europe and in Washington we were talking about how sanctions could be rolled back if and when the Minsk agreements were fully implemented," Nuland said, referring to a September ceasefire accord which has never been properly implemented.
"Now after the past week of flagrant violations of Minsk on both sides of the Atlantic we are forced to talk about the need to increase costs on Russia."
Indeed, EU leaders on Tuesday threatened new sanctions against Russia tasking their foreign ministers with considering tough new measures when they meet on the crisis on Thursday.
"We reject the narrative of grievance that is popular in Moscow today, that we wanted a weak Russia. Nothing could be further from the truth," Nuland said.
"What we wanted, what we still want, is a democratic Russia that respects rule of law at home and abroad."
The US diplomat, who has spearheaded US policy during the crisis in Ukraine, said Washington was also considering another $1 billion in loan guarantees this year -- on top of a similar guarantee last year -- if Kiev stays on course with its reforms.