Ukraine's largest rebel-controlled city of Donetsk was shaken by violence Wednesday as 10 people were killed, some of them teachers and parents showing up for the first day of school.
Terrified children were forced to shelter in the basement as the shelling yielded the highest single civilian toll since a tenuous ceasefire was struck between Kiev and pro-Russian separatists last month.
Clashes have raged for days at several flashpoints around the region, with both sides blaming the other for violating the agreement that commits them to withdrawing weapons and establishing a buffer zone.
The United States has decried the violence while the European Union decided Tuesday to keep Russian sanctions in place, maintaining pressure on Moscow in the worst East-West standoff since the Cold War.
The pro-Kiev regional government of Donetsk based in the government-controlled city of Mariupol accused pro-Russian separatists from the "Donetsk People's Republic" of shelling the school.
Four adults were killed, it said in a statement. Six more died when another shell struck a minibus at a bus stop about 500 metres from the school.
"I was going to open the doors to let passengers in and out when it happened," the driver of the vehicle, Mikhail Drobotun, told AFP as he sat on a gurney in a local clinic where dozens of the injured were being treated as artillery boomed in the background.
"I was injured in the leg, someone pulled me out," he said. "It hit the back of the bus."
AFP correspondents saw pools of blood at the deserted two-storey school, which is located about four kilometres away from the government-held Donetsk airport in an area that is frequently hit by shelling.
A source in Donetsk city hall told AFP that the strike happened right after the school's 70 pupils lined up for an assembly to mark the first day of class -- held nationally on September 1 but pushed back by rebel authorities because of the conflict.
Official rebel website DNR Today blamed the attack on Ukrainian artillery, claiming rebels do not possess the relevant weaponry and saying two security guards at the school were among the victims.
Russian media and separatist websites showed footage of rebels launching attacks from positions in apartment buildings near the airport.
Amnesty International in a statement urged Ukrainian and rebel forces to "immediately end indiscriminate attacks in residential areas", adding that both sides shared the blame for endangering civilians.
- Border patrols start -
The United States earlier decried the "intensifying violence" in eastern Ukraine and called on Russia and the rebels to hold fire.
"We call on Russia and the separatists it backs to immediately end these attacks" and on Moscow to withdraw its troops, State Department spokeswoman Jen Psaki said.
Jens Stoltenberg, the new NATO chief who took office Wednesday, argued in his opening remarks that "Russia maintains its ability to destabilise Ukraine" and "remains in breach of international law".
A delegation of about 70 Russian officers have however been working with Kiev since the weekend as part of a monitoring group.
Military spokesman Andriy Lysenko said that monitors, comprised of representatives from the Russian and Ukrainian militaries as well as the Organisation for the Security and Cooperation in Europe, have begun to patrol regions most frequently hit by ceasefire violations.
"Today the monitoring mission has begun work. They have begun patrols," he said of several groups consisting of six Russian officers, six Ukrainians and three to four representatives of the OSCE.
- Election season kicks off -
While the deaths lifted the toll to 68 since the truce deal was struck on September 5, Ukraine on Wednesday officially started its election season ahead of snap parliamentary polls on October 26.
Ukraine's central election commission said that nearly 3,500 candidates had registered for the election called last month by President Petro Poroshenko, more than a third of them as independents.
Poroshenko is also keen on holding the vote in the separatist regions, he stressed to Austrian Chancellor Werner Faymann who was in Kiev on a one-day visit.
"All of the points of the peace plan must be respected, including... holding elections on the territory of certain districts of Donetsk and Lugansk regions on December 7," he said after the talks.
However the separatists of Lugansk and Donetsk have vowed to boycott the polls and hold a vote of their own on November 2 for the regional leaders and legislative bodies.