An emergency session of the United Nations Security Council has meet at Russia's request after pro-Moscow forces came under attack from Ukraine's security forces in the country's eastern town of Slovyansk.

Vitaly Churkin, Russia's ambassador to the UN, accused the West in Friday's meeting of using double standards in dealing with the Ukraine crisis, claiming the Ukrainian government was using force against pro-Moscow civilians with the encouragement of the United States and the European Union.

The respresentatives of Western nations at the meeting, including ambassadors of UK, US and France, said they would not be "fooled by Russia", saying that the fact pro-Russian rebels shot down Ukraine's military helicopters was one of the clear indications that they were not civilians.

Gerard Araud, France's ambassador to the UN, said "Russia has opened a Pandora's box", but added that it was still possible to deescalate the situation in eastern Ukraine if Moscow withdrew its troops from the border.

Tensions are high after pro-Russia forces shot down two Ukrainian helicopters on Friday and Ukraine launched its first major offensive against an uprising in the east against Kiev's interim government.

Three pro-Moscow rebels, two Ukrainian military servicemen and two civilians were killed in the attack, according to information provided by the rebel spokeswoman and Ukranian defence ministry.

Ukraine's Western-backed government accuses Russia of fomenting the rebellion.

Lyall Grant, British ambassador to the UN, said before the meeting that the security council needed to keep "a very close eye monitoring events resulting from the destabilisation by Russia of eastern Ukraine".

The prospect for any council action is highly unlikely, as Russia holds veto power as a permanent council member.

Meanwhile, Barack Obama, US president, and Angela Merkel, German chancellor, agreed to impose "sectoral sanctions" on Russia if Moscow impeded plans for elections in Ukraine later this month.

Odessa clashes

In Odessa, a southern Ukrainian town, pro-Russians clashed with demonstrators for "United Ukraine" later on Friday, leaving at least one man killed and many injured.

Police said in a statement protesters had thrown petrol bombs, paving stones and "explosive devices" during the confrontation, and that at least 40 people died and scores were injured. The death score has included 38 people who died in the fire of trade union building, the statement said.

Meanwhile, Oleksandr Turchynov, Ukraine's interim president, said on Friday that Ukrainian border troops had rebuffed attempts by Russian "armed saboteurs" to cross into Ukraine overnight.

Russia's security service later denied the allegation.