UN Secretary-General Ban Ki-moon has voiced his alarm over the escalating Ukraine crisis in a phone call with Russian President Vladimir Putin.
"The Secretary-General ... underlined that any deepening of the crisis would be profoundly detrimental for all concerned; hence the need for everyone to work to de-escalate the situation," a statement from Ban's office read.
The United Nations Security Council will meet for an emergency session to discuss the crisis in eastern Ukraine today.
A diplomatic source has told Reuters the council will meet at 1am UK time at Russia's request.
Another diplomat has said negotiations are underway on Ukraine's participation.
Two consultants working for the United Nations, including one Briton were shot dead at Galkayo Airport in north central Somalia, a UN spokesman has said.
A UN spokesman said that the consultants were working for the United Nations Office on Drugs and Crime (UNODC).
A "devastating milestone" has been reached with one million Syrian refugees now in Lebanon which has had a "staggering" impact on the country, the United Nations said.
UN High Commissioner for Refugees Antonio Guterres said: "The influx of a million refugees would be massive in any country. For Lebanon, a small nation beset by internal difficulties, the impact is staggering.
"The Lebanese people have shown striking generosity, but are struggling to cope.
"Lebanon hosts the highest concentration of refugees in recent history. We cannot let it shoulder this burden alone."
Refugees from Syria now equal one quarter of Lebanon's population, according to UN figures.
Over half of all of Syria's chemical weapons inventory has been shipped out of the country, the United Nations and the Organisation for the Prohibition of Chemical Weapons have said.
It said a total of 53.6% of all chemical weapons material accounted for had been removed from or had been destroyed.
The group have asked to be given until April 27 to complete the full removal of the chemicals, which would put the mission two-and-a-half months behind schedule.
Russia may be preparing a further military incursion to Ukrainian territory, Ukraine's ambassador to the United Nations in Geneva, Yurii Klymenko, told UN diplomats at a briefing on the human rights situation in Ukraine, saying:
There are indications that Russia is on its way to unleash a full blown military intervention in Ukraine's east and south.
The statement was widely supported by other ambassadors, but challenged by a Russian diplomat, who read a prepared statement justifying Russia's actions so far.
Russia has vetoed a UN Security Council draft resolution that declared a planned referendum on the status of Ukraine's Crimea region "can have no validity" and urged nations and international organizations not to recognize it.
The Russian veto of the draft resolution, drawn up by the United States, was expected.
Moscow, which has sent military forces to the Crimea, is backing Sunday's referendum, which would transfer control of the region from Ukraine to Russia.
The brief resolution noted that the referendum was not backed by the Ukrainian government in Kiev.
"This referendum can have no validity, and cannot form the basis for any alteration of the status of Crimea," it states. It calls on "all states, international organizations and specialized agencies not to recognize any alteration of the status of Crimea on the basis of this referendum."
David Cameron is pushing for an independent, international investigation into alleged atrocities during the Sri Lankan civil war to begin within a year as pressure mounts on the regime in Colombo.
The Prime Minister has personally sought the support of several fellow leaders for a United Nations Human Rights Council resolution authorising a UN-led probe.
As many as 40,000 civilians are estimated to have died in the final months of the Sri Lankan government's 26-year fight with Tamil Tiger separatists - which ended in 2009.
Both sides in the brutal conflict are accused of widespread human rights abuses - including executions and rapes of prisoners by state troops.
US ambassador to the UN Samantha Power wrote on Twitter:
The proposed referendum on the future of #Crimea would violate the Ukranian constitution. The U.S. will not recognize its results.