Ukraine's president has appointed new officials to top defence posts as he pledged to stamp out the corruption that has left the country's armed forces faltering before a pro-Russian rebellion.

A statement published online late on Wednesday announced the appointments of colonel-general Valery Heletey as defence minister and lieutenant-general Viktor Muzhenko as chief of the military's general staff.

Poroshenko also appointed Yury Kosyuk, an agriculture magnate and one of Ukraine's richest men, to oversee defence issues in the presidential administration, and promised to "purge the army of thieves and fraudsters".

Accusations of corruption have been rife as Kiev's operation against the rebels continues.

Kiev has struggled to assert control over the country's industrial east, where fighting between government troops and pro-Russia separatists has killed more than 400 since April.

Meanwhile, foreign ministers from Russia, Ukraine, Germany and France agreed on Wednesday on a series of steps for a resumption of the ceasefire in eastern Ukraine where fighting between government troops and pro-Russia separatists has taken more than 400 lives since April.

The steps include reopening talks no later than Saturday "with the goal of reaching an unconditional and mutually agreed sustainable cease-fire'' to be monitored by the Organization for Security and Cooperation in Europe, their declaration said.

Fighting in eastern Ukraine has increased since a much-violated 10-day ceasefire expired late on Monday.

Source: Agencies