WASHINGTON (AFP) – Ukraine’s leader has told US Vice President Joe Biden that Russian-backed separatists continue to attack Ukrainian forces despite a unilateral ceasefire declaration, the White House said Sunday.

Western-backed President Petro Poroshenko ordered his forces to hold fire for a week on Friday as part of a broader peace plan aimed at ending the worst East-West standoff since the Cold War in the ex-Soviet state.

However, in a phone call Sunday, Poroshenko informed Biden that “Russian-backed separatists continued to attack Ukrainian forces, including with the use of artillery, following the ceasefire declaration,” the White House said in a statement.

Biden, welcoming the unilateral ceasefire declaration, “expressed concern that separatist leaders have refused to reciprocate,” the statement added.

And in a warning to the Kremlin, Biden said Washington was “working closely with its G7 partners to prepare further economic sanctions against Russia if Moscow did not take actions as described in the G7 leaders declaration to stop the flow of arms and militants across the border and use its influence to publicly call on the separatists to lay down their arms.”

The call came as Poroshenko and Russian President Vladimir Putin both called for dialogue and leaders in the self-proclaimed Donetsk People’s Republic reaffirmed that a “ceasefire unilaterally declared by the Ukrainian military without any coordination with us is not recognized by (our) militia.”

The Kremlin chief has been sending mixed signals to Kiev that included a surprise order Saturday for Russian forces stretching from the Volga to western Siberia to go on “full combat alert.”

Some analysts see the moves as a bid by Putin — still stunned at seeing months of deadly pro-EU protests lead to the February ouster of a Kremlin-backed president — to unsettle the new pro-Western team and keep reins on the Russified southeast while avoiding new Western sanctions.