A US official privy to negotiations is claiming major progress Tuesday, telling ABC News the Ukrainian delegation has agreed to the United States' potential peace plan, at a moment it's still being hotly debated, especially among the Europeans.

"The Ukrainians have agreed to the peace deal," the US official said, but without specifying much in the way of details. "There are some minor details to be sorted out but they have agreed to a peace deal."

Of course, the proverbial devil is in the details, along with each side's 'red lines' - and so this claim should be taken with caution at this still very early point.