A former senior aide to Russian President Vladimir Putin has warned that Ukraine will never be able to regain control over the separatist-controlled east.

Vladislav Surkov, who lost his job as Putin's adviser on Ukraine earlier this month, said in remarks published Wednesday that he stepped down because of a shift in the Kremlin course on the Ukrainian conflict. He didn't spell out specific reasons for his departure, saying only that it was due to a “change in context” on Ukraine.

Ukrainian President Volodymyr Zelenskiy has made settling the conflict in eastern Ukraine his top priority. December's summit of Russia, Ukraine, France and Germany failed to achieve a breakthrough, but the four leaders made a deal on a prisoner exchange and agreed on further moves toward settling the conflict in the east.

In this handout photo provided by the Ukrainian Presidential Press Office, Ukrainian President Volodymyr Zelenskiy speaks to media at a briefing after the Security Council meeting in Kyiv, Ukraine, Tuesday, Feb. 18, 2020. Ukraine and Russia-backed separatists are blaming each other for an outbreak of fighting in the country's rebel-held east. Ukraine's Army Chief of Staff Ruslan Homchak, right, and the Secretary of the National Security and Defense Council Oleksiy Danilov, left, listen. (Ukrainian Presidential Press Office via AP)

In this handout photo provided by the Ukrainian Presidential Press Office, Ukrainian President Volodymyr Zelenskiy speaks to media at a briefing after the Security Council meeting in Kyiv, Ukraine, Tuesday, Feb. 18, 2020. Ukraine and Russia-backed separatists are blaming each other for an outbreak of fighting in the country's rebel-held east. Ukraine's Army Chief of Staff Ruslan Homchak, right, and the Secretary of the National Security and Defense Council Oleksiy Danilov, left, listen. (Ukrainian Presidential Press Office via AP)

Asked Wednesday if the Russian policy on Ukraine has shifted, Putin spokesman Dmitry Peskov shrugged off Surkov's claim, saying that the Kremlin adheres to a 2015 peace agreement brokered by France and Germany as the basis for political settlement.

The conflict in Ukraine's industrial east, called Donbass, erupted in April 2014 — weeks after Russia's annexation of the Crimean Peninsula. More than 14,000 have been killed in fighting between Ukrainian forces and Russia-backed separatists.

Surkov hailed leaders of separatists in eastern Ukraine as “true warriors” and “real heroes.” He charged that Ukraine will never be able to restore its control over the rebel-controlled territories.

“Donbass doesn't deserve such humiliation,” he said. “Ukraine doesn't deserve such honor.”