The United States played down the chances of new sanctions on Russia while it assesses whether a deal to end the conflict in eastern Ukraine, including the withdrawal of Russian forces and equipment, is carried out.
The agreement envisages a cease-fire between Ukrainian forces and Russian-backed separatists taking hold from Sunday, the withdrawal of heavy weapons from the front lines and constitutional reform to give eastern Ukraine more political autonomy.
However, the deal struck by Germany, France, Russia and Ukraine was immediately followed by allegations from Kiev of a new, mass influx of Russian armor into rebel-held eastern Ukraine.
While saying it had not taken the possibility of new economic sanctions against Russia off the table, the U.S. government played down these concerns and held out the possibility of easing sanctions if Moscow carried out the agreement.
"The true test of today's accord will be in its full and unambiguous implementation, including the durable end of hostilities and the restoration of Ukrainian control over its border with Russia," the White House said in a statement that made no reference to the possibility of fresh U.S. sanctions.
"This agreement must now be followed by immediate, concrete steps to fulfill the commitments by all parties. The cease-fire must be implemented and honored. Heavy weapons must be withdrawn from the conflict zone, and Russia must end its support for the separatists and withdraw its soldiers and military equipment from eastern Ukraine," White House spokesman Josh Earnest added.
U.S. Secretary of State John Kerry held out the possibility of easing sanctions if the deal, which follows an earlier agreement also negotiated in Minsk, Belarus, was fully carried out.
"We will judge the commitment of Russia and the separatists by their actions, not their words," Kerry said in a statement. "As we have long said, the United States is prepared to consider rolling back sanctions on Russia when the Minsk agreements of September 2014, and now this agreement, are fully implemented."
The United States and European Union have imposed a series of sanctions on Moscow since Russia annexed Crimea from Ukraine in March.
In September, the United States hit Russia's largest bank, a major arms maker and arctic, deep water and shale exploration by its biggest oil companies with new sanctions.
U.S. State Department spokeswoman Jen Psaki said the United States had not taken fresh sanctions on Russia off the table but would prefer to see the cease-fire agreement carried out.