US Secretary of State John Kerry has accused Russian leaders of lying to him about Moscow's involvement in the conflict in Ukraine.
"Russia has engaged in a rather remarkable period of the most overt and extensive propaganda exercise that I've seen since the very height of the Cold War," Kerry told a Senate committee in Washington on Tuesday.
| Rebels look to strategic south
"And they have been persisting in their misrepresentations, lies, whatever you want to call them, about their activities there to my face, to the face of others, on many different occasions."
Kerry has met multiple times in European cities with Russian Foreign Minister Sergey Lavrov since the crisis erupted in early 2014.
Asked whether Moscow was lying when it denied that there were Russian troops or weapons in Ukraine, Kerry replied: "Yes."
The US administration is discussing whether to increase its support to Kiev to include lethal weapons to help the army battle pro-Russia rebels.
The Pentagon will deploy between five and 10 troops to western Ukraine to provide a second round of combat medical training to the Ukraine military there, a US military official told Associated Press on Tuesday.
Meanwhile, Britain's Prime Minister David Cameron announced that his country would also send servicemen to train Ukrainian forces.
"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.
Up to 75 military personnel will be deployed as part of an operation lasting up to six months, the defence ministry confirmed separately. This will exclude the supply of lethal equipment.
Meanwhile, Amnesty International released a report on Tuesday stating that illegal weapons have been used in the Ukrainian conflict by both sides.
"Taking into account everything we understand for now, we think that they [cluster bombs] were used by both sides,'' the right group's senior director for research, Anna Neistat, told reporters in Moscow.
In eastern Ukraine "both sides failed to take reasonable precautions to protect civilians, in violation of the laws of war,'' Amnesty International said.
Also on Tuesday, the foreign ministers of France, Germany, Russia and Ukraine met in Paris in a fresh push to salvage a crumbling peace plan for eastern Ukraine that they hammered out in the Belarusian capital, Minsk 12 days ago.