It is believed the bus had travelled from the
coastal town of Mariupol
A statement said the incident happened at a
government checkpoint in Buhas, about 35km (22 miles) south-west of
the rebel stronghold of Donetsk.
regional officials blamed pro-Russian rebels but a report
said rebel leaders had denied involvement.
intensified recently, despite a truce agreed in September.
One report said the bus
had been carrying civilians from the coastal
town of Mariupol.
Vyacheslav Abroskin, head
of the Donetsk regional interior ministry,
said it appeared the target had been a roadblock set up
close to the nearby town of Volnovakha
but the attack had gone wrong.
"It was a direct hit on an intercity bus,"
"An investigation is in progress.
The road between Donetsk and Mariupol has been
closed," he said.
reports said a shell had hit the bus, although a statement by
the military later said it could have
been a Grad rocket.
later said that 10 people were killed and
another two later died from their
injuries in hospital.
The Russian news agency Tass
quoted rebel officials as denying they had
carried out the attack.
Snow around the wreck of the bus was
stained with blood
Correspondents say government
forces and rebels frequently blame each other
for missile and artillery fire that claims
In a statement, Ukrainian
President Petro Poroshenko condemned the attack, blaming the
rebels and those "who is arming them and
inspiring to commit bloody crimes".
announced that on Wednesday he would order a
new wave of mobilisation in Ukraine.
The latest incident comes after
peace talks mooted for this week were
President Poroshenko said
in December that he planned to meet
Russian President Vladimir Putin in Astana, capital of Kazakhstan, on 15 January
alongside the German and French leaders.
talks in Berlin on Monday, foreign ministers
for the four countries said that "further work
needs to be done" before a summit could
They cited as
stumbling blocks the failure to implement the ceasefire
fully and the need to agree on how to
deliver aid and free prisoners.
More than 4,700 people have been killed
since the conflict began nine months ago.
Tuesday, the air traffic control tower at Donetsk airport
was destroyed amid renewed fighting.
The tower at Donetsk airport had been
battered by months of fighting
sides consider the airport strategically important but
it now lies in ruins after months of
shelling and artillery fire.
The BBC's Sarah Rainsford in Moscow says
that for many Ukrainians, the control tower
has become a symbol of resistance to the
In another development, the US Treasury said
it would provide a $1bn (£660m) loan guarantee to
Ukraine in the first half of 2015, provided Ukraine remained
on track to meet the conditions of its
loan from the International Monetary Fund.
has been pushed close to bankruptcy by
the separatist war in the east and huge debt repayments.
A US Treasury statement said that a
further $1bn loan guarantee could also be provided in
late 2015 "if conditions warrant".