U.S. Secretary of State John Kerry expressed "grave concern" to his Russian counterpart on Thursday over a sharp rise in separatist attacks in eastern Ukraine and urged an immediate ceasefire, the State Department said.
Kerry's comments, in a telephone call with Russian Foreign Minister Sergei Lavrov, reflected growing U.S. worries about the increasing violence between Ukrainian government forces and pro-Russian rebels.
A ceasefire deal, signed in mid-February in Minsk, has eased but not halted the violence in the eastern conflict zone. Both sides regularly accuse the other of violating the terms of the agreement and casualties are reported almost daily.
"The secretary expressed grave concern about the sharp increase in separatist attacks in Eastern Ukraine, and urged an immediate ceasefire and full implementation of Minsk obligations," the State Department said in a statement.
Moscow blames the Ukrainian authorities for the recent escalation in violence. The Russian Foreign Ministry said in a statement after the call that Lavrov stressed Kiev had to deliver on the Minsk agreements and "stop armed provocations."
In Washington on Monday, State Department spokesman John Kirby said the United States was "deeply troubled" by the rise in attacks, which he said had left three Ukrainian soldiers dead and 35 wounded in the past several days. Kirby said Ukraine had reported 127 attacks on Monday.
He also condemned a weekend arson attack that destroyed four vehicles in Donetsk belonging to OSCE (Organization for Security and Cooperation in Europe) monitors.
More than 6,500 people have been killed since fighting between Ukrainian troops and pro-Russian rebels seeking independence from Kiev erupted in April 2014, according to U.N. estimates.
In the phone call, Kerry also raised concerns about Iranian elite Quds force leader Qasem Soleimani's travel to Moscow, the State Department said. Soleimani has been subjected to an international travel ban and asset freeze by the U.N. Security Council since 2007.
Kerry and Lavrov also discussed options for a political solution to the Syria conflict, the State Department said.
The statement in Moscow said the two ministers discussed bringing various Syrian opposition groups together with the aim of working out their joint position for eventual talks Damascus under the U.N. auspices.
Two rounds of previous such talks in Switzerland have failed to find a solution to the conflict, which has killed some 250,000 people over the last four-and-a-half years.