UNITED NATIONS  - The US and Russia engaged in verbal clash over Ukraine at the UN late Sunday night after clashes between Ukrainian forces and pro-Russian separatists claimed their first casualty.

Russia called an emergency meeting of the UN Security Council on Sunday evening after another day of rising tension in eastern Ukraine with Kiev sending in the army to try and secure control of government buildings in a number of cities.

At the start of the meeting, a senior United Nations political official warned the 15-member Council that the crisis will only deepen unless intensive efforts are made by all sides to de-escalate the situation.

Once again, the situation in Ukraine has seriously deteriorated…and as of now, [the country] teeters on the brink,” UN Assistant Secretary-General for Political Affairs, Oscar Fernandez-Taranco said as he briefed an emergency meeting of the Council on the fallout from the latest escalation in the country, which began on 6 April, shattering two weeks of “relative” quiet.

He said that as the Council gathered for the 10th time this year to discuss this issue, Luhansk, Kharkiv and Donetsk and, in the last 24 hours, at least 5 other cities in Ukraine’s east have been targeted over by uprisings and the seizure of Government buildings.

Samantha Power, the US ambassador to the UN, accused Russia of orchestrating the recent protests and seizures of buildings in eastern Ukraine. “This is the saddest kind of instability – it is completely man-made,” she said. “This ‘instability’ was written and choreographed in and by Russia.” She added: “These are not protests, they are military operations.”

Vitaly Churkin, the Russian ambassador to the UN, denied that Moscow was involved in organising the protests. “It is the West that will determine the opportunity to avoid civil war in Ukraine,” he said. “Some people, including in this chamber, do not want to see the real reasons for what is happening in Ukraine and are constantly seeing the hand of Moscow in what is going on.”

Earlier, the Russian foreign ministry described the planned military operation to restore control of government buildings in Ukraine as “a criminal order”.

Oleksandr Turchynov, Ukraine’s acting president, said he had ordered armed forces to crack down on “terrorist troops co-ordinated by the Russian Federation” that had seized police and administrative buildings.

European foreign ministers are due to meet on Monday to discuss how to respond to the latest events and US vice-president Joe Biden is scheduled to visit Kiev next Monday.

Moscow warned that use of force by Kiev against separatists could foil plans to hold four-way talks this week with the US and EU to defuse the escalating crisis.

Sergei Lavrov, foreign minister, told US secretary of state John Kerry in a phone call over the weekend that the talks in Geneva on Thursday would be “undermined” if Kiev used force “against the residents of the southeast who have been driven to despair”.

Arsen Avakov, Ukraine’s interior minister, said at least one Ukrainian security official had been killed and several injured in gunfire in the city of Slavyansk. A Russian news agency reported that one pro-Russian militant had been killed and two injured.

As reports emerged of street battles and helicopters hovering over the city, the White House said it was worried about a “concerted campaign” to destabilise eastern Ukraine with the “apparent” support of Russia.

“We saw similar so-called protest activities in Crimea before Russia’s purported annexation,” Laura Lucas Magnuson, a national security council spokeswoman said. The Russian foreign ministry denied accusations that Moscow had instigated or was directly involved in the separatist insurgency.

Fernandez-Taranco said that UN monitors on the ground cited armed civilians on both sides, as well as militiamen armed with AK-47’s and sniper rifles among the “well-armed and well-organized” groups that consistently reinforced barricades along roads in the cities where the uprisings had occurred, adding that monitors also reported duelling protests where at least 50 people were apparently hurt.

He went on to tell the Council that as of today, at least one Ukrainian officer had reportedly been killed in the latest round of violence, but exact number of those injured during the skirmishes was not known as of now.

Amidst these events, he said, Ukraine’s Acting President Oleksandr Turchynov had issued a decree giving the self-declared separatists until 6:00 a.m. (local time) to give up their weapons in order to avoid prosecution.

Fernandez-Taranco said that Ukrainian authorities had vowed that if illegal activities are not halted, a full scale operation involving the Ukrainian army would be deployed. Russia has publicly stated on more than one occasion that it would be forced to act if Kyiv were to use force against demonstrators in the east.

“The situation is therefore now more combustible than ever,” he said, emphasizing that Secretary-General Ban Ki-moon and the UN remain committed to peaceful solution “to this ever deepening crisis”. Indeed earlier in the day, Ban had urged maximum restraint and adherence to international law.

He said the UN chief was also appealing for direct dialogue between the parties and between Kyiv and Moscow to de-escalate the situation. He was also calling on all those with influence on the parties to help resolve the crisis peacefully. “It has become painfully evident that the crisis will continue to deepen if intensive efforts are not urgently employed to de-escalate the situation,” he said.

Warning against a spillover of “potentially severe consequences,” Fernandez-Taranco said that if the concerned parties – and the world – do not come together to resolve the crisis, not only would Ukraine and Russia bear the brunt, European nations and the wider international community would be impacted as well.

Months of political unrest in Ukraine led to the removal by Parliament of President Viktor Yanukovych in February, followed by increased tensions in the country’s autonomous region of Crimea, where additional Russian military were subsequently deployed and a secession referendum was held in mid-March, in which the majority of the region’s people voted to join Russia.

Ban and other senior UN officials have been leading the push for a diplomatic resolution to the crisis. After returning from the region in late March, he called for a solution based on the principles of the UN Charter and warned the concerned parties – and the wider international community – that “at this time of heightened tensions, even small sparks can ignite larger flames of unintended consequences.”