Lithuania, Luxembourg and Sweden have explicitly backed Ukraine’s right to use force against pro-Russian separatists.

Lithuania’s UN envoy, Raimonda Murmokaite, and her Luxembourg counterpart, Olivier Maes, made the statements at a snap UN Security Council (UNSC) meeting in New York on Sunday (13 April).

Student or retired? Then this plan is for you.

“When the existence of the state is put in danger, we support the right of Ukraine to defend itself in the face of external aggression and to tackle militant separatism and continuous provocations,” Murmokaite said.

“Ukraine has the right to defend herself under article 51 of the United Nations charter,” Maes noted.

Sweden, which is not on the UNSC, added through its foreign minister, Carl Bildt, on Twitter: “If illegal armed groups took over police stations and local government offices in Sweden we would use all our instruments to restore order.”

The statements came hours before the expiry on Monday morning of an ultimatum issued by Ukraine’s caretaker government for armed pro-Russian separatists to cede control of government buildings in several cities in the eastern regions of Donetsk, Kharkiv, and Luhansk.

Ukraine said three people were already killed in clashes in the small hours of Monday on the outskirts of Slaviansk and in Slaviansk city centre.

The UNSC meeting was called by Russia, which, according to the US and the UK, has 40,000 elite troops massed on the Ukrainian-Russian border.

The Russian UN envoy, Vitaly Churkin, urged Wesern powers to stop Kiev from taking action.

“Let’s concentrate attention on what we can do – in this case I'm directing my eyesight at my Western colleagues – in order to prevent the Kiev authorities’ reckless actions, which at this moment are embodied in the criminal order of [acting Ukrainian president] Mr. Turchynov, and to prevent the realisation of this order, which will have the most severe implications primarily for the people of Ukraine,” he said.

He described the Kiev authorities as “national radicals and chauvinists, Russophobic, anti-Semitic forces” and threatened to call off a meeting between the EU, Russia, Ukraine and the US in Geneva on Thursday.

Churkin got limited support from UNSC member Rwanda, whose envoy, Eugene-Richard Gasana, said: “Rwanda remains of the view that military action will only worsen the already tense situation.”

But Australia, France, the UK and the US joined the smaller EU states in condemning Russia’s actions.

Commenting on the escalation in eastern Ukraine since 6 April, the US’ Samantha Power said: “We know who is behind this. Indeed, the only entity in the area capable of these co-ordinated, professional military actions is Russia.”

Britain’s Mark Lyall Grant noted: “The international community is not fooled by the Kremlin’s use of propaganda and misinformation . . . what we are witnessing is a well-orchestrated campaign designed to destabilise the country.”

He described Russia's actions as “tactics drawn from the darkest days of the last century”.

France’s Gerard Araud also complained about Russia’s massive hike in Ukraine gas prices and its blockade of Ukrainian exports in recent days. “The economic pressure is biting more and more,” he said.

The EU and US have threatened to impose economic sanctions on Russia and to blacklist more Russian officials if it invades mainland Ukraine.

But EU foreign ministers meeting in Luxembourg on Monday are not ready to go ahead if the crisis escalates suddenly.

The ministers are still waiting for the European Commission to prepare a sanctions options paper, due mid-week, among disagreement between EU countries on how far to go.

"I don't think we'll see tier-three [economic] sanctions tomorrow, but it's very difficult to envisage not seeing anything after the events of the weekend," a Western diplomatic source told Reuters on Sunday.

"The real question will be to see whether [EU] member states agree to ask [the EU foreign service] to prepare an additional list of restrictive measures,” a senior EU official told the news agency.