Russia's 'invasion' of Ukraine alienates EU friends

“We have repeatedly made ​​clear that any further escalation must of course lead to a discussion about further sanctions”, she noted.

Her office added that she called US president Barack Obama the same day and that they “agreed that such [Russian] behaviour should not remain without consequences”.

French president Francois Hollande in a speech to his ambassadors in Paris on Thursday morning said: "If it turns out to be true that Russian soldiers are present on Ukrainian soil, that would of course be intolerable and unacceptable”. He added that EU sanctions should be “increased, if [Russia] continues to escalate”.

Italian PM Matteo Renzi, who phoned Russian leader Vladimir Putin, said afterwards in a communique that Russia’s actions are “an intolerable escalation whose consequences would be very serious”.

Germany, France, and Italy have in the past blocked more robust EU action due to their business links with Russia, while Merkel last week had indicated that she was willing to make concessions on EU-Ukraine free trade if Putin backs off.

The more hawkish Western leaders also spoke out on Thursday.

Obama told press in Washington: “We are not taking military action to solve the Ukrainian problem. What we’re doing is to mobilise the international community to apply pressure on Russia”.

“In our consultations with our European allies and partners, my expectation is, that we will take additional steps”.

UK leader David Cameron said: “We urge Russia to pursue a different path … If [she] does not, then she should be in no doubt that there will be further consequences”.

Estonian president Toomas Ilves called Russia’s actions “an undeclared war” on Ukraine, adding that “Western allies should agree on their part on the need to intervene in an even more determined way”.

The harsh words were echoed at a snap meeting of the UN Security Council (UNSC) in New York.

The German UN embassy noted that out of the 15 UNSC members “all but one [Russia] … condemn the recent military escalation”.

Alexis Lamek, the French UN envoy, said Russia’s actions “will not be tolerated”.

Samantha Power, the US ambassador to the UN, noted: “The most important question for us now is not what we should say to Russia. The most important question is what we should do to make Russia listen”.

She added that the existing Russia sanctions have hurt EU and US economies, but “if unchecked, the damage that Russia’s blatant disregard for the international order poses is much, much greater”.

The UK’s Mark Lyall Grant reeled off evidence of Russia’s increasing military presence in Ukraine, saying: “Russia can no longer pretend that it is not a direct party to this conflict”.

The Lithuanian UN ambassador, whose country called for the UN meeting, said the Western response so far to Russia’s “creeping attack against Ukraine” has been “like that of the proverbial boiling frog” - referring to the cliche of a frog in a pot which does not jump out and dies because the water heats up slowly.

But the Russian UN envoy, Vitaly Churkin, hit back, saying he is “shocked by the barrage of criticism and distortion of the facts” by his fellow UN members.

He accused the UNSC of trying to “whitewash” crimes by the Ukrainian military and told the US to “stop interfering in the internal affairs of sovereign states”.

The sharp words came after Russian forces this week joined rebels in a new offensive in south-east Ukraine in what Ukrainian diplomats and some EU ministers have called an overt “invasion”.

Nato publishes images

Nato also on Thursday released fresh satellite images of Russian mobile artillery and other units on the move inside its neighbour.

A senior Nato officer, Dutch brigadier general Nico Tak, told press there are “substantial numbers of Russian combat troops inside Ukraine”, adding that “Russia's ultimate aim is to alleviate pressure on separatist fighters in order to prolong this conflict indefinitely”.

Any extra EU sanctions are likely to be matched by Nato action at its upcoming summit in Wales next week.

The alliance’s secretary general has said it will create a rapid reaction force with permanent facilities in eastern European Nato states to counter potential Russian aggression against countries such as Estonia or Latvia.

Russia’s dismembering of Ukraine has also caused alarm in Finland and Sweden. The two countries, which have stayed out of Nato in order not to antagonise Russia, said this week they will sign “host nation” agreements with the alliance to enable it to station troops on their territory.

Finland on Thursday complained that Russian military planes keep entering its airspace in an apparent campaign of intimidation.

Helsinki put the Finnish airforce on alert, with foreign minister Erkki Tuomioja saying: “The violations must stop”.

“Three airspace violations within a week is a lot and unfortunately they [Russia] don’t really have a good explanation. What we know is they are done somewhat on purpose. We don’t know what that purpose is”, Finnish defence minister Carl Haglund added.