The long-awaited pullback is a precondition for the first face-to-face talks between Russian President Vladimir Putin and Ukraine's Volodymyr Zelensky, to be mediated by the leaders of France and Germany.

"The process of troop withdrawal began by both sides... in the area of Zolote-4" in the Lugansk region, Ukraine's army said on Facebook.

Monitors from the Organisation for Security and Cooperation in Europe confirmed the move.

"Today the sides have just resumed the withdrawal of troops and arms in Zolote," Martin Sajdik, an OSCE special representative, told journalists.

The rival forces also need to withdraw troops from the village of Petrivske in the Donetsk region for the high-profile summit to go ahead.

- 'Surrender' -

Since coming to power in May, comedian-turned-president Zelensky has sought to revive a peace process to end a five-year-old separatist conflict in eastern Ukraine that has claimed some 13,000 lives.

But those efforts have stalled as Kiev's forces and the Kremlin-backed separatists have repeatedly failed to pull back troops from the frontline because of exchanges of gunfire.

Zelensky's peace plan including the troop pullback has been strongly criticised by many in Kiev, especially war veterans and nationalists.

Over the past few weeks, thousands of Ukrainians including Zelensky's predecessor Petro Poroshenko have protested in the capital Kiev and other cities, slamming a pullback of troops as an act of "surrender."

Nationalists were set to hold a new protest rally outside Zelensky's offices on Tuesday evening.

Various nationalist organisations even deployed their own troops to Zolote in an effort to prevent a retreat of Ukrainian forces.

Last week the 41-year-old Ukrainian president was forced to personally travel to Zolote in an effort to convince his nationalist critics not to stand in the way of the peace process.

"We have to look for ways and work to end the war," Zelensky said Saturday during his trip to the village.

"There will be no surrender in any case... I am sure we will succeed and Ukraine will be united again."

- Special status -

Putin's aide Vladislav Surkov expressed satisfaction about the move.

"If everything works out in Zolote, similar procedures in Petrivske should follow immediately," he told Russian TASS news agency.

Political opponents were quick to criticise Zelensky on Tuesday.

Ivanna Klympush-Tsintsadze, a lawmaker from Poroshenko's party, called the troop withdrawal a "capitulation on the Kremlin's conditions".

Another opposition party Golos condemned Zelensky for breaking his own promise to withdraw troops only after fighting stops for seven days, while there was shooting across the frontline as recently as the weekend.

"The withdrawal of troops without fulfilling the conditions of the 7-day silence regime is unacceptable," the party said in a statement.

"Such actions of the president and his team are a mistake," it said.

In the run-up to the planned summit, Ukrainian, Russian and separatist negotiators also agreed on a roadmap that envisages a special status for the separatist territories if they conduct free and fair elections under the Ukrainian constitution.

Critics say the proposal favours Russia but Zelensky has pledged not to betray Ukraine's interests.

Ties between Ukraine and Russia were shredded after a bloody uprising ousted a Kremlin-backed regime in 2014.

Moscow went on to annex Crimea and support insurgents in eastern Ukraine.

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