Russia in turn has warned it could within days cut off gas supplies to Ukraine -- and, by extension, to parts of the European Union.
For the first time since the European-brokered truce came into force February 15, no deaths were reported in Ukraine's war zone by either side for the past 24 hours.
"Over the past day, one soldier was wounded but there were no dead," Ukrainian military spokesman Andriy Lysenko told journalists in Kiev.
Rebels insisted they were withdrawing artillery, rocket launchers and tanks from some areas, and journalists saw a column of howitzer guns being driven along a road near the separatist stronghold of Donetsk.
"We are following orders to pull back heavy weapons, but the Ukrainians aren't," a rebel commander going by the nickname "Khoroshii" told AFP.
But the OSCE mission in Ukraine said in a statement the warring sides had not provided the information needed to determine what, if any, arms withdrawals have occurred.
The West has thrown its hopes of finding a negotiated solution to Ukraine's 10-month conflict fully behind the truce, which last week won unanimous backing from the UN Security Council.
But continued breaches by rebel forces -- especially their assault on Debaltseve, a strategic transport hub, and a build-up and attacks on Ukrainian army positions near the port city of Mariupol -- have exasperated the EU and US.
