A missile struck a passenger bus near a town in eastern Ukraine on Tuesday, leaving 11 civilians dead and 17 wounded, officials said.
It was not clear who was responsible for the deadly attack near the town of Volnovakha. Both Ukrainian law enforcement officials and pro-Russia separatists locked in a simmering armed conflict in parts of the Donetsk region blamed one another.
The bus was making a regular trip from Donetsk to Mariupol when it was hit by a Grad missile shortly after 2 p.m., Vyacheslav Abroskin, the Donetsk region police chief, wrote on his Facebook page.
Investigators were working at the site, he said.
"After having seen this with my own eyes I can say those who did this are not human but beasts without principles and morals," Abroskin wrote. "They must be destroyed."
The UNIAN news agency ran a number of graphic images from the site of the tragedy, depicting the yellow bus riddled with shrapnel, its windows gone, metal sides and ceiling twisted and the curb nearby awash with blood.
The bus was hit in front of a Ukrainian army checkpoint. Later in the day, a separatist website reported that "a checkpoint of the punitive forces was destroyed near Volnovakha."
The item was taken off the website after the reports of civilian casualties emerged.
Andrei Purgin, the self-proclaimed Donetsk People's Republic parliament speaker, was quoted by Russia's RIA Novosti news agency as saying that the separatists didn't have the means to mount a missile attack in that area.
"The Ukrainian side needs to investigate what happened deep in its own territory," he said. "It was far away from [the front line]."
Another separatist leader, Denis Pushilin, called it "a provocation" and warned of an impending advance of Ukrainian troops allegedly preparing to violate the shaky truce that has been in effect since September.
In a late-night address posted on the presidential website, President
"Being proponents of peace, we are ready to defend our land," Poroshenko said. He added that Ukraine had "grown muscles" during the truce by resupplying troops and repairing equipment.
"Tomorrow, I will sign a decree about another wave of mobilization," Poroshenko said. "I am convinced the Ukrainian people will support this decision and the mobilization will be a success."
The separatists have significantly intensified shooting at Ukrainian army positions since Jan. 9, Bogdan Bondar, a senior officer with the Ukraine General Staff, told the national parliament in Kiev. He also used the term "provocation" to describe the attack.
Ukrainian army and law enforcement forces have come under fire 67 times since 6 a.m. on Tuesday, Bondar said.
In mid-December, the United Nations said the death toll from fighting in eastern Ukraine was over 4,700, with about 10,000 wounded.