"The forces of the 'anti-terrorist operation' are preparing for the final stage of liberating Donetsk. Our forces have completely cut Donetsk off from Luhansk. We are working for liberating both towns but it's better to liberate Donetsk first - it is more important," Lysenko told Reuters news agency.
The Ukraine military has been steadily closing in on the pro-Russian separatists since a week-long ceasefire ended on July 1. The army's planned move on the city comes as the mayor of Donetsk said that overnight shelling struck a high-security prison, killing one convict was killed and allowing 106 others to escape.
Mortar blasts rocked the correctional facility in a western district of the city on Sunday evening, hitting living areas, administrative headquarters and an electrical substation, the city council said in a statement.
One prisoner died and fifteen more received light wounds, AFP news agency reported. Meanwhile, the bombardment also sparked a mass jail break that saw scores of detainees flee the prison. By Monday morning an unspecified number had been returned to the facility and a more precise figure would be given by evening, the statement added.
A growing number of civilian casualties have been reported as artillery bombardments have hit hospitals and homes around the city. Both sides have been criticised for causing the casualties by firing indiscriminately in populated areas.
Russia had previously called for a ceasefire to allow a humanitarian mission in to help civilians, but the West warned that this could be used as guise to send in an invasion of ground troops.