As Ukraine's military and Russia-backed separatists blamed each other for the continued attacks, US Secretary of State John Kerry and British Foreign Secretary Philip Hammond held Moscow responsible. Kerry accused the Russians of "land-grabbing" in Ukraine while cynically speaking of peace.
The top American diplomat pointed specifically to the strategic port of Mariupol, which Ukrainian forces say is threatened by a buildup of rebel military equipment. If the rebels seize the city, they would establish a land corridor between mainland Russia and the Russia-annexed Crimean Peninsula.
The message to Russian President Vladimir Putin's government, he said, would be: "We're not going to play this game. We're not going to sit there and be part of this kind of extraordinarily craven behavior at the expense of the sovereignty and integrity of a nation."
Ukrainian forces today reported attacks over the past day that killed a serviceman and wounded 40, with mortars reaching the fringes of Mariupol, among other places. The rebels said Ukrainian forces shelled 15 locations overnight, including parts of Donetsk, the largest separatist-controlled city.
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The US has warily backed the diplomatic effort despite little faith in the Kremlin changing course. Washington repeatedly has invoked the threat of new sanctions if Russia doesn't cut off the separatists.
Economic measures against Russia in the past year has severely damaged the country's economy, but done little to change the calculus of Putin's government in Ukraine.
It's unclear whether the US has sufficient support among its partners in Europe for a new round of trade or financial restrictions. Europe's participation is seen as necessary, given its far deeper economic relationships with Russia.
"We will talk about how we maintain European Union unity and US-European alignment in response to those breaches," Hammond said.