Kiev: A UN-backed ceasefire showed signs of finally taking hold in Ukraine on Wednesday, with no deaths reported on the front for the first time since the truce took effect 10 days ago.
However, Secretary of State John Kerry told US lawmakers: "To date, neither Russia nor the forces it is supporting have come close to complying with their commitments," renewing warnings that Moscow would face further sanctions.
A day earlier, Kerry had said the Russians were persisting in "lies... to my face" about their activities in Ukraine. The US dismisses Moscow`s denials about giving military backing to the separatists in east Ukraine.
Russia has in turn warned it could cut off gas supplies to Ukraine within days -- and, by extension, to parts of the European Union.
The geopolitical tensions between the old Cold War foes overshadowed a lull in fighting that produced the first day without fatalities since the ceasefire came into effect on February 15.
"Over the past day, one soldier was wounded but there were no dead," Ukrainian military spokesman Andriy Lysenko told journalists in Kiev. The rebels also reported no deaths on their side.
There was still no confirmation, though, from the Organization for Security and Cooperation in Europe (OSCE) of a pull-back of heavy weapons from the frontline -- the other key plank of the truce.
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.
But the OSCE mission in Ukraine said the warring sides had not provided the information needed to determine what, if any, arms withdrawals have occurred.
Kiev says it will not carry out an arms pull-back until a full and "comprehensive" ceasefire is observed and has accused Russia of continuing to send military hardware in to bolster the rebels. The West has thrown its hopes of finding a negotiated solution to the 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 attacks on Ukrainian army positions near the port city of Mariupol -- have exasperated the EU and US.
British Prime Minister David Cameron this week announced his country will send up to 75 soldiers to Ukraine on a "training mission". He said they would not be sent to the conflict zone.
Poland on Wednesday announced its own plans to send a small contingent of troops to Ukraine to help train Kiev`s military officers.
Cameron urged the EU to look at wide-ranging sanctions on Russia`s economy, which is already toppling into recession because of a drop in oil prices.
Russia, though, is flexing its muscles in readiness for any additional sanctions.
Its state-run gas giant Gazprom has warned it could cut off supplies to Ukraine, amid a dispute over payment.
President Vladimir Putin said Wednesday that Ukraine had paid only enough "for three or four days` gas supplies. Unless there is a prepayment, Gazprom... will terminate the supply," according to the Interfax news agency.
Much of the gas that flows through Ukraine goes on to supply the EU market.
Putin, in televised comments, also claimed Ukraine had cut off gas supplies to separatist-held territories in the east in what "smacks of genocide."The instability is torpedoing Ukraine`s fragile economy. The country`s central bank on Wednesday increased currency controls in a bid to stop a free-fall of the hryvnia.
Also of concern to EU neighbours is a Russian military drill launched near the borders with Estonia and Latvia.
Some 1,500 Russian paratroopers were to descend from the skies en masse in an exercise to capture and destroy an enemy`s airfield, defence ministry spokeswoman Irina Kruglova told AFP. She said the drill was to continue into Saturday.
Since the start of the Ukraine crisis, Russia has staged a series of wargames that have alarmed its post-Soviet neighbours and the West.
Lithuania said on Tuesday it would return to limited conscription later this year because of "the current geopolitical environment".