Ukrainian authorities said an artillery shell has hit a trolley bus in the eastern city of Donetsk, killing at least eight people and sparking accusations of blame from both Ukraine and Russia. Earlier reports had put thе number of dead at 13.
"Russian terrorists today again committed a terrible act against humanity, and the Russian Federation bears responsibility for this," Ukraine's Prime Minister Arseniy Yatsenyuk said in a statement published on the government's website.
Russia reponded with similar terms.
"We regard the incident [in Donetsk] as a crime against humanity [and a] gross provocation," Russia's Foreign Minister Sergei Lavrov said in a statement published on the ministry's website.
Lavrov also called for an independent investigation of the incident in the city that has been at the center of a territorial struggle between Ukrainian troops and pro-Russia separatists.
Amnesty International denounced what it called the "appalling loss of civilian life." The London-based human rights group added that a "thorough, impartial and independent investigation into this possible violation of the laws of war is needed immediately."
Meanwhile, pro-Russian separatists paraded a group of captured Ukrainian servicemen Thursday at the bus stop where the trolley bus was hit. Some of the captured servicemen were reportedly abused by local residents.
A Ukrainian military spokesman denied government troop involvement in the bus attack, saying their closest position is too far away from Donetsk for its artillery to have reached the area of the incident.
Meanwhile, Ukrainian military authorities say its troops have withdrawn from most of Donetsk airport after months of struggle to keep control over the structure that has taken on symbolic significance in a conflict that to date has claimed more than 4,800 lives.
NATO: more signs of Russian involvement
NATO has expressed renewed concern Thursday over an escalation in fighting and what it sees as heightened Russian involvement in the conflict in eastern Ukraine.
“The situation along the line of contact in Ukraine is not good. The fighting has intensified to essentially pre-agreement or pre-standdown levels and in some cases beyond,” said NATO’s top military commander, U.S. General Philip Breedlove, referring to a September truce deal which called on both sides to pull back their forces.
A pro-Russia separatists' tank is seen in a fortified position at a check-point north of Luhansk, eastern Ukraine, Jan. 14, 2015.
Breedlove also pointed to new signs of a Russian presence on Ukrainian territory.
“We are beginning to see the [heat] signatures of air defense systems and electronic warfare systems that have accompanied past Russian troop movements into Ukraine,” said Breedlove at news conference in Brussels after a meeting of NATO defense chiefs.
NATO has previously cited evidence which it said pointed to the presence of Russian troops in eastern Ukraine, but Breedlove said he could not confirm Ukrainian President Petro Poroshenko's recent estimate of 9,000 Russian soldiers on Ukrainian soil.
Breedlove also announced that alliance military leaders would try to re-establish contacts with their Russian counterparts, broken off as a result of tensions over Ukraine.
US denounces Putin ‘peace plan’
Meanwhile, the United States has denounced a peace plan on Ukraine put forth by Russian President Vladimir Putin as an “occupation plan.”
“It is time to pull the veil away from Putin’s peace plan and call it for what it is – a Russian occupation plan,” said U.S. Ambassador to the U.N. Samantha Power, speaking at a Security Council meeting late Wednesday.
“Time and again President Putin has extended an olive branch in one hand, while passing out grad missiles and tanks with the other,” added Power, reiterating Western accusations that Russia has been providing military hardware for separatist rebels in eastern Ukraine, a charge the Kremlin denies.
Moscow says Putin sent Ukrainian President Petro Poroshenko new peace proposals last Thursday. A Kremlin spokesman subsequently said that the Ukrainian leader rejected them. Ukrainian media has been reporting that the new plan contained proposals which in effect would allow Russia to extricate itself from commitments it made under a broader peace agreement it signed in September in Minsk, Belarus.
Responding to Power’s accusations, Russia’s U.N. Ambassador Vitaly Churkin blamed Washington and Kyiv for the latest escalation in fighting in eastern Ukraine, saying that “the United States has been playing a destructive role [in the Ukrainian crisis]."
'Land grab' accusation
On Wednesday, U.S. Secretary of State John Kerry accused pro-Russian separatists in eastern Ukraine of violating an earlier truce deal with "a blatant land grab" in new fighting near the Russian border.
Kerry spoke Wednesday alongside European Union foreign policy chief Federica Mogherini in Washington. He called the new fighting "an alarming situation," adding that rebels have violated a deal they signed in September by extending their control of disputed territory more than 500 square miles (1,300 square kilometers).
Earlier Wednesday, Ukraine's president linked the new fighting - much of it near the rebel-controlled cities of Donetsk and Luhansk - to what he said was the recent deployment of more than 9,000 regular Russian troops into Ukraine's territory.
Speaking at an economic forum in Davos, Switzerland, Petro Poroshenko said the Kremlin has also sent more than 500 tanks, heavy artillery and armored personnel carriers into eastern Ukraine. He renewed his demand that Russia seal its border and withdraw all of its forces.
Some material for this report came from Reuters and AFP.