Vladimir Putin has boasted that he could take the Ukrainian capital Kiev in "two weeks", according to reports of a telephone conversation between Russia's president and the outgoing European commissioner.
Putin, who has repeated his categorical denial that Russian troops are in Ukraine, despite evidence to the contrary from Ukraine's leadership, has been defiant in recent days about Moscow's right to protect its interests in the country.
The respected Italian daily La Repubblica reported that in a conversation with outgoing European Commission President José Manuel Barroso, Putin remarked: "If I want, I take Kiev in two weeks."
The Russian leader was just as belligerent when cornered by the BBC's John Sweeney at a mammoth museum at Russia's Northeastern Federal University in Yankutsk. Maneuvering past the tank-sized bodyguards, Sweeney came face-to-face with Putin, repeatedly asking if he "regrets the killings in Ukraine".
Attempting to defer, Putin eventually replied in Russian. “What is the aim and sense of today’s military operation in the east? And what triggered the escalation of their activities,” the president said.
“They are triggered by the fact that Ukrainian troops are laying siege to civilian areas and are shooting directly at residential areas. “This is what many states, including in Europe, unfortunately prefer not to notice."
The president was clearly riled by the confrontation, dismissively stopping his translator in mid-sentence at one point, to reply to Sweeney directly in English.
Separately, speaking at the Moscow State Institute of International Relations on Monday, Russian foreign minister Sergei Lavrov also denied his country had staged a military intervention, and shrugged off warnings of yet tougher sanctions from the West.
In the House of Commons today, David Cameron denounced the presence of Russian troops on Ukrainian soil as "unjustified and unacceptable" and accused Moscow of trying to force its smaller neighbour to "abandon its democratic choices at the barrel of a gun".
Cameron later told MPs it was important Russia saw British troops in nearby Nato countries. "I think it's very important that when Russia looks at countries like Estonia or Latvia or Poland they don't just see Estonian, Latvian and Polish soldiers, they see French, German, British soldiers too.
Heavy fighting is ongoing in eastern Ukraine as talks began in the Belarussian capital Minsk between the Kiev government and separatist leaders. Pro-Russia leaders, despite declaring "independence" after questionable referendums earlier this year, are believed to be receptive to staying as part of Ukraine as long as there is a substantial regional devolution of power and guarantees about the status of the Russian language in Ukraine.
The Ukrainian army was on Monday forced to abandon the airport in the city of Luhansk, because they came under fire from what a military spokesman said was a Russian tank battalion. According to a morgue doctor in Luhansk who spoke to Human Rights Watch, explosive weapons have killed more than 300 civilians in the city since May.
On Sunday, European leaders ordered officials to make urgent preparations for a toughening of measures, likely to target senior Kremlin figures as well as the defence, energy and financial sectors, as Putin urged talks about the future of the country's volatile east, as pro-Russia separatists, apparently bolstered by Russian fighters, clash with the Ukrainian army.
Ukraine should launch discussions with the separatists "not about technical issues but about the question of the political organisation of society and statehood in south-east Ukraine, with the goal of safeguarding the legitimate interests of those people who live there," Putin said in a speech this weekend.
The use of the word "statehood" led many to question if Putin had hinted that he would support the separatist movement, but aides were quick to clarify that Putin did not envision sovereignty for the two separatist eastern regions that style themselves as "Novorossiya" or New Russia.
Although Ukraine is not a member of Nato, its president Petro Poroshenko will join leaders of Nato nations at this week's summit in Wales, and British troops will take part in a series of large-scale exercises in former Eastern Bloc countries in an effort to demonstrate the alliance's commitment to them.
Lithuanian president Dalia Grybauskaite, whose country used to be part of the Soviet Union, has suggested EU states should be supplying Kiev with military equipment.
"It is the fact that Russia is in a war state against Ukraine," she told reporters. "That means it is in a state of war against a country which would like to be closely integrated with the EU. Practically Russia is in a state of war against Europe.
"That means we need to help Ukraine to ... defend its territory and its people and to help militarily, especially with the military materials to help Ukraine to defend itself because today Ukraine is fighting a war on behalf of all Europe."
Nato secretary general Anders Fogh Rasmussen unveiled a new Readiness Action Plan, including proposals for a new force of several thousand troops to act as a "spearhead" to be deployed at very short notice to help member states defend themselves against any threat, including Russia.
Backed by air and naval assets, the unit would be made up of troops contributed on a rolling basis by the 28 Nato member states, including the UK. A senior Nato official said that it was envisaged that the force could respond within two days of a threat, and elements of it could be in place by the end of this year.
"I cannot say you will see all of the elements in place by Christmas, but some parts of it will be," said the source.
Speaking in Brussels, Mr Rasmussen said: "The Readiness Action Plan will ensure that we have the right forces and the right equipment in the right place, at the right time.
"Not because Nato wants to attack anyone. But because the dangers and the threats are more present and more visible. And we will do what it takes to defend our allies."