KYIV, Ukraine--Ukrainian President Volodymyr Zelenskyy said no one knows how long the war in his country will last but that Ukrainian forces are defying expectations by preventing Russian troops from overrunning eastern Ukraine, where the fighting has been fierce for weeks.

In his nightly video address, Zelenskyy said he was proud of the Ukrainian defenders managing to hold back the Russian advance in the eastern Donbas region, which borders Russia and where Moscow-backed separatists have controlled much of the territory for eight years.

“Remember how in Russia, in the beginning of May, they hoped to seize all of the Donbas?” the president said late Saturday. “It’s already the 108th day of the war, already June. Donbas is holding on.”

After failing to capture Kyiv, Ukraine’s capital, early in the war, Moscow has focused on seizing the parts of the largely Russian-speaking Donbas still in Ukrainian hands, as well as the country’s southern coast. Russian forces have been drawn into a long, laborious battle, thanks in part to the Ukrainian military’s use of Western-supplied weapons.

Sievierodonetsk, an eastern city with a prewar population of 100,000, is still being hotly fought over, both sides said. The city and neighboring Lysychansk are the last major areas of the Donbas’ Luhansk province not under the control of the pro-Russia rebels.

Leonid Pasechnik, the head of the separatist-declared Luhansk People’s Republic, said Ukrainian fighters remained in an industrial area of the city, including a chemical plant where civilians had taken shelter during a weeks-long Russian bombardment.

“Sievierodonetsk is not completely 100 percent liberated,” Pasechnik said, claiming that Ukraine was shelling the city from the Azot plant. “So it’s impossible to call the situation calm in Sievierodonetsk, that it is completely ours.”

Luhansk Gov. Serhii Haidai reported that a big fire broke out at the plant Saturday during Russian shelling. Haidai said Sunday on the Telegram messaging app that Russian forces were still shelling the chemical plant and destroyed a second bridge connecting Sieverodonetsk and Lysychansk.

He did not address how many soldiers or civilians were holed up in the plant.

A Luhansk People’s Republic’ official, Rodion Miroshnik, said that 300 to 400 Ukrainian troops remained blockaded inside the Sievierodonetsk chemical plant along with several hundred civilians. He said efforts are underway to try to evacuate the civilians but the troops will be allowed to leave only if they lay down their arms and surrender.

To the north of the city, Russian shelling of settlements in the Kharkiv region killed three people, Gov. Oleh Syniehubov said Sunday.

The Russian military said Sunday it destroyed a large weapons depot in western Ukraine, while local officials said missile strikes had injured civilians.

Russian Defense Ministry spokesman Igor Konashenkov said long-range, sea-based Kalibr missiles had hit “a large depot of anti-tank missile systems, portable air defense systems and shells supplied to the Kyiv regime by the U.S. and European countries” near the city of Chortkiv in the western Ukrainian region of Ternopil.

Ternopil governor Volodymyr Trush said missile strikes on Chortkiv injured 22 people, including seven women and a 12-year-old boy. Trush said four Russian missiles, launched Saturday evening, partially destroyed a military facility and damaged four residential buildings.

Elsewhere in Ukraine, a counteroffensive pushed Russians out of parts of the southern Kherson region they took early in the war, according to Zelenskyy.

Moscow has installed local authorities in Kherson and other occupied coastal areas, offering residents Russian passports, airing Russian news broadcasts and taking steps to introduce a Russian school curriculum.

Zelenskyy said while an end to the war was not in sight, Ukraine should do everything it can so the Russians “regret everything that they have done and that they answer for every killing and every strike on our beautiful state.”

The Ukrainian leader asserted that Russia has suffered about three times as many military casualties as the number estimated for the Ukrainian side, adding: “For what? What did it get you, Russia?”

There are no reliable independent estimates of the war’s death toll so far.

Speaking at a defense conference in Singapore on Sunday, Chinese Defense Minister Gen. Wei Fenghe said Beijing continues to support peace talks between Russia and Ukraine and hopes the U.S. and its NATO allies have discussions with Russia “to create the conditions for an early ceasefire.”

“China will continue to play a constructive role and contribute our share to easing tensions and realizing a political resolution of the crisis,” Wei said.

He suggested that nations supplying weapons to Ukraine were hindering peace by “adding fuel to the fire” and stressed that China had not provided any material support to Russia during the war.

The Institute for the Study of War, a think tank based in Washington, said Ukrainian intelligence suggested the Russian military was planning “to fight a longer war.” It cited the deputy head of Ukraine’s national security agency as saying that Moscow had extended its war timeline until October.

The intelligence “indicates the Kremlin has, at a minimum, acknowledged it cannot achieve its objectives in Ukraine quickly and is further adjusting its military objectives in an attempt to correct the initial deficiencies in the invasion,” the think tank said.

Pasechnik, the separatist leader, said the Ukrainians making a stand in Sievierodonetsk should save themselves the trouble.

“If I were them, I would already make a decision (to surrender),” he said. “We will achieve our goal in any case.”