The United Nations Security Council has called a rare emergency special session of the 193-member General Assembly on Russia’s invasion of Ukraine, as Western allies step up a diplomatic campaign to isolate Moscow.

The vote by the 15-member council was procedural so Russia could not wield its veto.

A resolution convening the General Assembly session was adopted with 11 yes votes. Russia voted no, while China, India and the United Arab Emirates abstained.

“The members of this council have laid bare Russia’s diplomatic impotence. Russia again was isolated,” Britain’s UN Ambassador Barbara Woodward said.

“Russia cannot stop the world from coming together to condemn its invasion of Ukraine.”

The move is the latest in a flurry of diplomacy at the United Nations in New York.

It followed a Russian veto on Friday of a draft council resolution that would have deplored Moscow’s invasion of Ukraine. China, India and the United Arab Emirates abstained and the remaining 11 members voted yes.

It also came as Ukraine agreed to attend negotiations with Moscow’s delegates on the Belarus border and Russian President Vladimir Putin moved his nuclear weapons defences to “special alert”.

Mr Putin said on Sunday he was putting Moscow’s nuclear forces on a “special regime of combat duty” in response to “aggressive statements” coming from Western powers.

The General Assembly, which will meet on Monday (Australian time), is expected to vote on a similar resolution as soon as Wednesday, US Ambassador to the United Nations Linda Thomas-Greenfield said. No country has a veto in the General Assembly.

“Russia cannot veto our voices. Russia cannot veto the Ukrainian people. And Russia cannot veto the UN Charter,” Ms Thomas-Greenfield said.

“Russia cannot, and will not, veto accountability.”

While the assembly’s resolutions are non-binding, they carry political weight.

Action at the United Nations is viewed as a chance to show Russia is isolated because of its invasion of neighbouring Ukraine.

They will be looking to improve on the 100 countries who voted in favour of a General Assembly resolution in March 2014 after Russia annexed Ukraine’s Crimea region.

That resolution declared invalid a referendum on the status of Crimea.

The vote will be come at the end of the emergency special session. It will be only the 11th such General Assembly session convened since 1950.

“Any attempt to circumvent the position of a Russian Federation, any attempt to disregard it, undermines the very bedrock of the UN Charter,” Russia’s UN Ambassador Vassily Nebenzia said of the Security Council votes on Friday and Sunday.

France’s UN Ambassador Nicolas de Riviere said his country would put forward a draft council resolution “to demand the end of hostilities, protection of civilians, and safe and unhindered humanitarian access to meet the urgent needs of the population.”

Russia would be in a position to block the move if it chooses. It has council veto power along with the United States, France, Britain and China.

-with AAP