President Petro Poroshenko will nominate his fourth defence minister of the year Monday, after dismissing the incumbent ahead of high-level talks with Moscow aimed at bringing peace to the Western-backed former Soviet state.

Poroshenko's official website said he would nominate a new defence chief after "accepting the resignation" of Valeriy Geletey, who was only appointed in July.

The sacking highlighted a sense of failure that has enveloped the once-proud force as the six-month conflict with pro-Russian rebels drags on and the death toll from fighting approaches 3,400.

The military's performance has humiliated Ukrainians who had been celebrating the success of a bloody popular uprising that ousted the then Kremlin-backed leader in February and propelled Kiev on its Westward course.

Geletey's removal threatens to undermine Poroshenko's position ahead of a crunch meeting with Russian President Vladimir Putin in Milan on Friday that will also include German Chancellor Angela Merkel.

The Kremlin said Merkel -- a vocal Poroshenko ally who helped arrange the two leaders' first meeting on the sidelines of a Normandy summit in June -- called Putin on Sunday "to discuss preparations" for Milan.

Poroshenko told the nation he had "no illusions" going into his fourth meeting with Putin since rising to power in May.

"These will not be easy negotiations, but I am ready for them," Poroshenko said in a Sunday evening television address.

"My goal (is) our country's unshakable independence, its territorial integrity, the inviolability of its borders, and the return of peace," he said.

Putin appeared to strengthen his hand with the order on Saturday for 17,600 Russian troops deployed near Ukraine to return to their bases -- a decision analysts linked to his desire to see biting Western sanctions suspended or at least rolled back.

- Eastern bloodbath -

There had been some speculation about Poroshenko's displeasure with Geletey's ability to organise a decisive assault on the insurgents since his appointment on July 3.

The respected Dzerkalo Tyzhnia weekly said Geletey's fate was sealed when he received a report on August 23 of an incursion by hundreds of Russian special forces and dozens of armoured vehicles into the eastern war zone -- allegations that Moscow denied.

The newspaper quoted a military commander as saying that Geletey ignored the intelligence and instead took part in an Independence Day parade in central Kiev the next day.

The alleged military deployment was followed by a sweeping counter-offensive that saw separatist gunmen quickly seize back a chunk of the land they had lost in the preceding weeks.

The militias also wiped out a Ukrainian unit of at least 100 soldiers near the town of Ilovaysk. The bloodbath shocked the country and soon saw Poroshenko sign a Russian-backed peace pact with the rebel command.

The September 5 truce agreement was designed to create a buffer zone along the front line and grant the insurgents limited autonomy within Ukraine.

But neither side has pulled back their big guns or halted all fire.

Militias across the Russian-speaking rustbelt are still attacking Ukranian forces and the number of civilians killed daily by stray shells and rockets is nearing that seen at the height of the six-month war.

The ongoing fighting could damage Poroshenko's chances in October 26 parliamentary elections that feature a powerful group of parties opposing any talks with Moscow.

- Russian withdrawal -

The Kremlin says that Putin has ordered back the soldiers from Ukraine's border simply because their scheduled summer training period had run its course.

But Moscow has repeatedly used its troop movements as a bargaining chip with the West over Ukraine's future in the past.

Analysts said the withdrawal order will be cited by Russian Foreign Minister Sergei Lavrov when he tries to convince US Secretary of State John Kerry in Paris on Tuesday that the West's economic restrictions were no longer justified.

The troop pullback may also be designed to splinter the united, tough stance that Washington and Brussels forged after months of EU foot-dragging over sanctions against Moscow.

Some European nations with close energy and financial ties to Russia blame the weakness of their economic recoveries on the trade war that Moscow launched in reprisal for the Western punitive steps.