KIEV, Ukraine -- Ukrainian President Petro Poroshenko on Monday publicly lifted his objections to a referendum that could give more powers to the restive regions engulfed in more than a year of warfare, reversing his government's previous position. Russia-backed separatists, however, dismissed Poroshenko's gesture as meaningless.

The conflict between Russia-backed rebels and government troops in eastern Ukraine has claimed more than 6,000 lives. When it began, protesters in the east demanded a vote on giving their regions more autonomy. Such calls were rejected by the Ukrainian government at the time.

But Poroshenko on Monday met a parliamentary commission that is drafting amendments to the country's constitution and said in a televised meeting that if the commission decides a referendum is necessary, he wouldn't stand in the way.

"I'm ready to launch a referendum on the issue of state governance if you decide it is necessary," he said. The president added that he was sure Ukrainians would support a strong, unitary state.

Poroshenko on Monday insisted that he still opposed federalization, which Russia has advocated, but favours decentralizing power in favour of the regions. Decision-making on security, defence and foreign policy, Poroshenko said, would remain in the hands of the central government.

In Washington, U.S. State Department spokeswoman Marie Harf welcomed Poroshenko's remarks as part of decentralization efforts intended "to bring the government closer to the people and to strengthen regional and local institutions."

Poroshenko said he still opposes making Russian a second official language, vowing that "Ukrainian has been and will be our only state language."

Senior rebel official Andrei Purgin said Poroshenko's insistence shows that "he doesn't listen to the voice of the east: we speak Russian here."

Purgin dismissed Poroshenko's referendum proposal as meaningless, adding that Kyiv's refusal to invite rebel representatives to join the constitutional commission indicated its reluctance to negotiate.

"Kyiv's actions signal its desire to dictate its terms to us rather than a desire to reach agreement," Purgin told The Associated Press.

Ukraine's eastern industrial heartland was the support base for Kremlin-friendly President Viktor Yanukovych, who was ousted in February last year after months of protests. The rebellion, which flared up in the east a year ago following Russia's annexation of Crimea, claimed more than 6,000 lives.

Hostilities have subsided in the region since February's cease-fire deal between Ukraine and the Russia-backed rebels, and the parties have pulled their heavy weapons back from the frontline and exchanged prisoners.

On Monday, the rebels have freed 16 Ukrainian prisoners. Poroshenko confirmed their release on Twitter.

However, attempts at a political settlement have stalled.

Prime Minister Arseniy Yatsenyuk on Monday dismissed suggestions of direct talks with the rebels.

"When we talk about our dialogue with the east, we mean a dialogue with legitimately elected representatives of the east of the country, not Russian gangsters and terrorists."

Moscow sided with the rebels, strongly urging Kyiv to include them in deliberations on constitutional reform. Russian Foreign Minister Sergei Lavrov said Monday that reform should go ahead "only with the approval and agreement of Luhansk and Donetsk," the two biggest cities under separatist control.