Ukraine's government has signalled its intention to press on with military operation, as pro-Russian rebels try to regroup after losing their stronghold.
President Petro Poroshenko, drawing confidence from the fall of the rebel bastion of Slovyansk at the weekend, named on Tuesday a new chief of military operations in the troubled eastern region.
Earlier, he also appointed a new defence minister who ruled out negotiations until the separatists laid down their arms.
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One rebel leader played down the loss of Slovyansk as a military expedient, and said the hundreds of fighters who were able to move from the town to the regional capital Donetsk were preparing to defend that city and hit back.
"We're not preparing ourselves for a siege. We are preparing ourselves for action," Alexander Borodai, prime minister of the self-proclaimed Donetsk People's Republic, told a Russian online newspaper during a visit to the Russian capital, Moscow.
Sporadic shooting was heard from various parts of Donetsk overnight though no specific incidents were reported.
But in Luhansk, a city on the border with Russia where rebels also control key buildings, two people in a minibus were killed by a shell that exploded nearby, a municipal official said.
Poroshenko named Vasyl Grytsak to head the "anti-terrorist centre", making him operational chief in the drive to crush the rebels.
Grytsak, a 53-year-old police lieutenant-general and 20-year veteran of the state security apparatus, replaces Vasyl Krutov, who had headed the "anti-terrorist centre" since mid-April.
Barely one month after assuming office, Poroshenko has appointed a hardline defence minister in a move to shake-up the military and security leadership to bring fresh vigour in the fight against the insurgency.
Krutov and other security officials have come under criticism for the patchy performance of the armed forces and big military losses including the downing of a military plane by the rebels.
Pro-Russian rebels have been fighting government forces since April when they set up separatist republics in the Russian-speaking east.
The fall of Slovyansk to government forces has now swung the focus onto Donetsk, raising the question of how the Kiev military will go about breaking the resistance in a sprawling industrial city with a population of over 800,000.
Armed men have been out on the streets, setting up new barricades and checkpoints and stopping pedestrians and motorists to run spot identity checks.
Borodai, the leader of rebels, brushed off suggestions that Slovyansk had been a defeat, portraying it as a successful tactical withdrawal, though Kiev says the rebels sustained heavy losses.
Two bridges were destroyed on Monday after Ukraine's deputy security council chief said forces would blockade the cities Donetsk and Luhansk.
But Borodai scoffed at talk of Kiev having the resources to do this.
The Ukrainian army's victory in Slovyansk has pushed peace talks involving separatist leaders off the agenda.
The new defence minister, Valery Heletey, in remarks reported on Tuesday, said there could be no fresh talk of a ceasefire until the rebels had laid down their arms.