Oleksandr Turchynov said his government would mobilize the army if necessary in a bid to regain control of several eastern towns and cities where pro-Russian militants have seized strategic state buildings. Speaking on national television, the interim president also promised amnesty from prosecution to any militants who laid down their weapons by Monday morning.
"The Security Council has made a decision to begin a large-scale anti-terrorist operation with the participation of army forces," Turchynov said. "We are not going to allow Russia to repeat the Crimean scenario in Ukraine's east."
The acting president offered further details of an apparent gunfight outside Slovyansk, first reported by interim Interior Minister Arsen Avakov. Turchynov said that a Security Service of Ukraine member was killed and two other officers wounded in the incident.
In reference to the attack, Turchynov said that "blood has been spilt in a war that is being waged against Ukraine by Russia."
The Russian foreign ministry in Moscow called Turchynov's announcement a "criminal order," saying in a statement that it was "now the West's responsibility to prevent civil war in Ukraine."
The statement also said that Russia would move to urgently add the latest developments in Ukraine to the United Nations Security Council agenda. A UN spokesman on Sunday evening confirmed via his Twitter feed that the Security Council would convene in New York at 8 p.m. local time (0000 UTC on Monday).
Ukraine's interim authorities say that it is the Kremlin that is behind the current unrest in several eastern municipalities such as Slovyansk, perhaps most notably the major industrial city of Donetsk. The US ambassador to the UN, Samantha Power, said in an interview with American broadcaster ABC that these allegations appeared accurate.
Power said that the actions in eastern towns and cities had "all the tell-tale signs of what we saw in Crimea: It's professional, it's coordinated, there's nothing grassroots-seeming about it. The forces are doing - in each of the six or seven cities that they've been active in - exactly the same thing."
The US ambassador also told the "This Week" program that further economic sanctions against Russia were a possibility "if actions like the kind we've seen over the last few days continue."
Geneva talks approaching
Representatives from Russia, Ukraine, the European Union and the US are scheduled to meet in Geneva on Thursday for diplomatic talks. German Foreign Minister Frank-Walter Steinmeier on Sunday described the situation in Ukraine as highly dangerous, saying he hoped for no interruptions in the coming days which could put the talks at risk.
Steinmeier's counterpart in Russia, Sergei Lavrov, had previously warned that violence against the Russian-speaking Ukrainian population could jeopardize the negotiations. Speaking to German public broadcaster ARD, Steinmeier also sounded a note of caution.
"Above all, there's one thing we ought not do now: to overburden this first meeting of the big four in Geneva," the German foreign minister said, calling the simple agreement to sit down for talks "a small breakthrough."
msh/pfd (AFP, AP, dpa, Reuters)