US secretary of state John Kerry told Russian foreign minister Sergei Lavrov in a telephone call on Tuesday that Washington would impose more sanctions on Russia if tensions did not de-escalate in eastern Ukraine, a senior US official said.
The official said Kerry talked to both Lavrov and Ukrainian prime minister Arseny Yatseniuk.
"With foreign minister Lavrov, the secretary expressed deep concern over the lack of positive Russian steps to de-escalate, cited mounting evidence that separatists continue to increase the number of buildings under occupation and take journalists and other civilians captive," he said.
"He urged Russia to tone down escalatory rhetoric, engage diplomatically in the east with the OSCE and Ukrainian government, and issue public statements calling for those occupying buildings to disarm and stand down in exchange for amnesty," he added.
The official said Kerry also reiterated that the absence of measurable progress on implementing last week's Geneva agreement would result in increased sanctions on Russia.
In Moscow, the Russian foreign ministry said Lavrov had told Kerry that Ukraine must take urgent steps to implement the Geneva agreement aimed at defusing the Ukraine crisis.
The US official said Kerry had told Yatseniuk that Kiev must take important steps as well to de-escalate tensions, "including progress on amnesty legislation, steps toward broadening the national dialogue on constitutional reform to include representatives of all regions and close coordination with the OSCE monitoring mission."
Washington has said it would decide "in days" on additional sanctions if Russia does not take steps to implement the agreement.