PARIS (AFP) - The United States (US) and Russia failed on 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, Mr 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.

"We expressed divergent positions on the reasons for the Ukraine crisis," Mr Lavrov said.

"Nevertheless we agreed on the need to find points of agreement to reach a common position in order to resolve this crisis diplomatically," Mr Lavrov told reporters.

In Russia's view, such a solution would involve Ukraine becoming a federalist state and guarantee the rights of its Russian minority, Mr Lavrov indicated.

"We are convinced that federalism is a very important element of the constitutional reforms (Kiev must implement)," he said.

"We have to find a consensus, a compromise between the regions of Ukraine.

"It is us up to the Ukrainians to resolve these questions. The authorities in Kiev have to set equal conditions for each region to participate in a process of constitutional reform.

"We agreed (with the US) to work with the Ukrainian government and the Ukrainian people in the broadest sense to enable measures to be taken in the following priority areas: assuring the respect of minority rights, language rights, the dismantling of irregular forces and provocateurs and the achievement of an inclusive process of constitutional reform."