The United Nations Security Council held an emergency session on Sunday night to discuss the escalating crisis in Ukraine, just hours before a deadline by Kiev for pro-Russian separatists to disarm by Monday morning or face a "full-scale anti-terrorist operation" by its armed forces.
The Council began meeting at 8 p.m. at Russia's request after Moscow called Kiev's plans to mobilize the army to put down a rebellion by pro-Russian militants in eastern Ukraine "criminal."
Britain's U.N. ambassador said Russia had massed tens of thousands of well-equipped troops near the Ukrainian border in addition to the 25,000 troops it recently moved into Crimea, which Moscow seized last month.
"Satellite images show that there are between 35,000 and 40,000 Russian troops in the vicinity of the border with Ukraine equipped with combat aircraft, tanks, artillery and logistical support units," Ambassador Mark Lyall Grant said.
"This is in addition to the 25,000 Russia troops based illegally in Crimea," Lyall Grant added in his speech during the U.N. emergency meeting.
Angered by the death of a state security officer and the wounding of two comrades near the flashpoint eastern city of Slaviansk, Ukrainian acting president Oleksander Turchinov gave rebels occupying state buildings until 0600 GMT (2 a.m. EDT) to lay down their weapons.
"The National Security and Defense Council has decided to launch a full-scale anti-terrorist operation involving the armed forces of Ukraine," Turchinov said in an address to the nation.
He blamed Russia, which annexed Ukraine's Crimea region when Moscow-backed former president Viktor Yanukovich fled after months of pro-Western protests, for being behind the rash of rebellions across Russian-speaking towns in eastern Ukraine.
"We will not allow Russia to repeat the Crimean scenario in the eastern regions of Ukraine," Turchinov said.
The deadline and the standoff with Russian troops at the border have raised fears of a military confrontation with Moscow.
The head of Ukraine's state security service (SBU) said government forces would respond ruthlessly if pro-Russian separatists opened fire.
"If they open fire, we will annihilate them. There should be no doubt about this," Valentyn Nalyvaichenko said in a televised interview.
Russia's Foreign Ministry called the planned military operation a "criminal order" and said the West should bring its allies in Ukraine's government under control.
"It is now the West's responsibility to prevent civil war in Ukraine," the ministry said in a statement.
The 15-nation council has held numerous emergency meetings on Ukraine but has been incapable of taking any concrete action because of Russia's sharp disagreements with the United States and Europe.
Earlier, the American ambassador to the U.N., Samantha Power, said on ABC's "This Week" that the United States was prepared to step up sanctions against Moscow if pro-Russian military actions in eastern Ukraine continued.
"The president has made clear that, depending on Russian behavior, sectoral sanctions in energy, banking, mining could be on the table, and there's a lot in between," she added.
Ukraine has repeatedly said the rebellions are inspired and directed by the Kremlin. But action to dislodge the armed militants risks tipping the stand-off into a new, dangerous phase as Moscow has warned it will protect the region's Russian-speakers if they come under attack.
One Ukrainian state security officer was killed and five were wounded on the government side in Sunday's operation in Slaviansk, Interior Minister Arsen Avakov said. "There were dead and wounded on both sides," he wrote on his Facebook page.
The separatists are holed up in the local headquarters of the police and of the state security service, while others have erected road blocks around Slaviansk, about 150 km (90 miles) from the Russian border.
Kiev accuses the Kremlin of trying to undermine the legitimacy of presidential elections on May 25 that aim to set Ukraine back on a normal path after months of turmoil.
However, Russian Foreign Minister Sergei Lavrov said Kiev was "demonstrating its inability to take responsibility for the fate of the country" and warned that any use of force against Russian speakers "would undermine the potential for cooperation", including talks due to be held on Thursday between Russia, Ukraine, the United States and the European Union.
US ready to step up sanctions on Russia
The United States is prepared to step up sanctions against Moscow if pro-Russian military actions in eastern Ukraine continue, the US envoy to the United Nations said yesterday.
Pro-Russian activists seized government buildings on Saturday in the eastern town of Slaviansk. Ukrainian security forces were trying to oust the activists.
The American ambassador to the UN, Samantha Power, said on ABC's "This Week" that the latest events in Ukraine bore "the telltale signs of Moscow's involvement."
She said sanctions already imposed by the US had an impact: the Russian ruble has fallen to an all-time low, the country's stock market has depreciated by 20 percent and investors are fleeing the country.
"The president has made clear that, depending on Russian behavior, sectoral sanctions in energy, banking, mining could be on the table, and there's a lot in between," Power said. "I think we've seen that the sanctions can bite, and if actions like the kind we've seen over the last few days continue, you're going to see a ramping up of those sanctions."
Asked if Russian President Vladimir Putin wants to seize eastern Ukraine, Power said his actions "give credence to the idea." Power said the rebellion has "all the telltale signs of what we saw in Crimea. It's professional, it's coordinated ..."
Republican Senator John McCain said the Obama administration's failure to punish Russia over Crimea had only emboldened Putin.
"The question is now, What do we do and what does he do?" he said. "It's obvious that he is encouraged by the fact that we sanctioned a few people and suspended - didn't even throw him out - of the G8."
McCain repeated his calls for tougher sanctions and for giving Ukrainians light weapons so they can defend themselves.
"They didn't fight in Crimea," he said. "But if he starts moving in further encroachment in this way into eastern Ukraine, they will fight."
Ukraine launches "anti-terrorist" operation
The Ukrainian government on Sunday launched an "anti-terrorist" operation in an eastern city where armed pro-Russian men seized police and security services buildings, Interior Minister Arsen Avakov said.
"An anti-terrorist operation has begun in Slavyansk. It is being directed by the anti-terrorist center of the state security service. Forces from all the security units of the country have been brought in," Avakov was quoted by the Interfax news agency as saying on his Facebook page.
He said the men who seized the buildings opened fire on the approaching troops, adding that both sides had suffered casualties during the raid.
"There are deaths and injuries on both sides. On our side -- an SBU (Ukrainian Security Service) officer. The head of the SBU's anti-terrorist center has been wounded, as have four others," he said. "On the side of the separatists -- an unidentified number."
Avakov said the special forces had begun to "regroup" and urged local residents to remain calm and stay at home as a safety precaution.
"Pass this on to all civilians: they should leave the center of town, not come out of their apartments, and not go near the windows," he said.
The Ukrainian government's move came one day after about a dozen gunmen seized a police headquarters and the Security Service office in Slavyansk amid simmering tensions in the country's Russian-speaking regions.
A new wave of unrest erupted in Ukraine's east last weekend, when pro-Moscow activists seized several government buildings in the cities of Donetsk, Lugansk and Kharkov, demanding a referendum on autonomy and closer ties with Russia.
On March 18, Russian President Vladimir Putin and Crimean leaders signed a treaty to make the southern peninsula part of Russian territory after almost 97 percent of Crimean voters backed secession from Ukraine in a referendum.
Kiev has rejected the referendum and Crimea's integration with Russia, saying it was unconstitutional.
Ukrainian presidential candidate suggests postponing elections till autumn
Popular lawmaker and candidate for Ukraine's presidency Oleg Tsaryov believes the presidential elections should take place in autumn, after provisions about the federative framework and the national status of the Russian language would be added to the Constitution of Ukraine.
"The minimal term is autumn. Until autumn, they should vote for amendments to the Constitution, and after they fulfill all our conditions, we would be ready to take part in these elections," the nominee said.
Tsaryov urged people from southeastern Ukraine to consolidate and make joint demands to the country's leadership, which, as he believes, must enter into negotiations with the protesters and listen to them.
Earlier, the lawmaker agreed to lead the Southeastern movement for federalization. Only by federalizing Ukraine, it is possible to "save the country from breaking up", the politician pointed out at a news conference in Donetsk.
