In a recent phone call to his Russian counterpart Sergey Lavrov, U.S. Secretary of State John Kerry again called for de-escalation in Ukraine and urged Lavrov to encourage separatist fighters to put down their weapons.

According to U.S. State Department Spokesperson Jen Psaki, Kerry pressed Lavrov "to end all support for separatists, denounce their actions and call on them to lay down their arms," and then pushed Moscow "to reach out to President-elect Petro Poroshenko and begin working together to de-escalate the conflict."

Kerry also raised concerns about reports of foreign fighters crossing the border from Russia into Ukraine, particularly reports of Chechen fighters, said Psaki.