The United States and Russia failed Sunday to reach a deal on Ukraine but Russian Foreign Minister Sergei Lavrov said talks here with US Secretary of State John Kerry had been "constructive" and would continue. After four hours of discussions, Lavrov said the two parties had presented their plans for a de-escalation of the crisis but did not agree on what had caused it. He reiterated Russia's belief that federalism in Ukraine would be key to finding a solution.