A U.N.-backed ceasefire showed signs of taking hold in Ukraine on Wednesday, but tensions remained high after the U.S. accused Russia of "lies" and Britain ordered a small troop deployment to train Kiev's forces.

Russia in turn has warned it could within days cut off gas supplies to Ukraine -- and, by extension, to parts of the European Union.

Up to 2,000 Russian soldiers took part in drills in the country's west on Wednesday as Moscow conducted an inspection of its paratrooper units in the latest show of strength likely to alarm its neighbors.

Some 500 units of equipment were also to be included in drills in the western Pskov region which borders EU members Estonia and Latvia, defense ministry spokeswoman Irina Kruglova told AFP.

The United States expressed fury at Russia's "lies" over Ukraine after European powers urged a frayed ceasefire be respected, while a rare overnight calm was reported in the war zone on Wednesday.

But the crisis still simmered dangerously. Britain said it was dispatching a team of soldiers to Ukraine for "training" and warned Russia could be cut off from the SWIFT international banking network, while Russia's Gazprom is threatening to stop gas supplies to Ukraine.

France, Germany, Russia and Ukraine called Tuesday for a total ceasefire in eastern Ukraine as London announced it was sending troops to train government forces fighting pro-Russian separatists in eastern Ukraine.

British Prime Minister David Cameron said his country would send up to 75 military personnel to advise and train Kiev forces, but ruled out sending lethal equipment as "there needs to be a diplomatic solution" to the conflict.

The president of the International Committee of the Red Cross spoke out Tuesday against "politicizing" the issue of humanitarian assistance for war-torn eastern Ukraine.

Speaking to reporters after meeting Russian President Vladimir Putin to discuss the Ukraine crisis, Peter Mauer also called on Moscow and Kiev to create what he called a common "humanitarian space."

Britain will send troops to Ukraine next month to train government forces fighting pro-Russian separatists, Prime Minister David Cameron announced Tuesday, while ruling out sending lethal equipment.

"Over the course of the next month we are going to be deploying British service personnel to provide advice and a range of training, from tactical intelligence to logistics to medical care, which is something else they have asked for," Cameron told a parliamentary committee.

Lithuania said Tuesday it would return to limited conscription later this year as concern mounts over Russian military exercises near NATO Baltic states.

"We must temporarily renew mandatory military service," President Dalia Grybauskaite told reporters.

Russia's state-owned gas giant Gazprom warned Tuesday it could cut off gas deliveries to Ukraine within two days, upping the stakes in the crisis there -- and threatening supplies to the rest of Europe.

The Gazprom announcement came hours ahead of a Paris meeting of the foreign ministers of Russia, Ukraine, Germany and France.

Despite pressure from sanctions and a high-level Franco-German mediation, the conflict in east Ukraine shows little sign of ending, Lithuania's foreign minister said Monday.

"Despite all these efforts, the situation has almost not changed," Linas Linkevicius told Agence France Presse in an interview. "We do not see any effect."

Britain on Monday criticized Russia for failing to enforce the terms of a tattered truce in eastern Ukraine in the face of ongoing attacks by pro-Russian separatists. 

"I have to say from the experience of the last 10 to 12 days, the Russian engagement in the Minsk process is rather cynical," British Foreign Secretary Philip Hammond said in the Estonian capital Tallinn.