Russian forces pounded the city of Lysychansk and its surroundings in an all-out attempt to seize the last stronghold of resistance in eastern Ukraine's Luhansk province, the governor said Saturday.

Ukrainian fighters have spent weeks trying to defend the city and to keep it from falling to Russia, as neighboring Sievierodonetsk did a week ago. The Russian Defense Ministry said its forces took control of an oil refinery on Lysychansk's edge in recent days, but Luhansk Gov. Serhiy Haidai reported Friday that fighting for the facility continued.

“Over the last day, the occupiers opened fire from all available kinds of weapons,” Haidai said Saturday on the Telegram messaging app. Luhansk and neighboring Donetsk are the two provinces that make up the Donbas region, where Russia has focused its offensive since pulling back from northern Ukraine and the capital, Kyiv, in the spring.

Pro-Russia separatists have held portions of both eastern provinces since 2014, and Moscow recognizes all of Luhansk and Donetsk as sovereign republics. Syria's government said Wednesday that it would also recognize the “independence and sovereignty” of the two areas and work to establish diplomatic relations with the separatists.

In Slovyansk, a major Donetsk city still under Ukrainian control, four people died when Russian forces fired cluster munitions late Friday, Mayor Vadym Lyakh said on Facebook. He said the neighborhoods that were hit didn't contain any potential military targets.

The leader of neighboring Belarus, a Russian ally, claimed Saturday that Ukraine fired missiles at military targets on Belarusian territory several days ago but all were intercepted by the air defense system. President Alexander Lukashenko described it as a provocation and noted that no Belarusian soldiers are fighting in Ukraine. There was no immediate response from the Ukrainian military.

Belarus hosts Russian military units and was used as a staging ground for Russia's invasion. Last week, just hours before Lukashenko was to meet with Russian President Vladimir Putin, Russian long-range bombers fired missiles on Ukraine from Belarusian airspace for the first time.

Lukashenko has so far resisted efforts to draw his army into the war. But during their meeting, Putin announced that Russia planned to supply Belarus with the Iskander-M missile system and reminded Lukashenko of how dependent his government is on economic support from Russia.

Elsewhere in Ukraine, investigators combed through the wreckage from a Russian airstrike early Friday on residential areas near the Ukrainian port of Odesa that killed 21 people.

Ukrainian Prosecutor-General Iryna Venediktova said the investigators were recovering fragments from missiles that struck an apartment building in the small coastal town of Serhiivka. They also were taking measurements to determine the trajectory of the weapons and "the specific people guilty of this terrible war crime,” she said.

Ukrainian President Volodymyr Zelenskyy said three anti-ship missiles struck “an ordinary residential building, a nine-story building” housing about 160 people. The victims of Friday's attack also included four members of a family staying at a seaside campsite, he said.

'I emphasize: This is deliberate direct Russian terror, and not some mistake or an accidental missile strike," Zelenskyy said. The British Defense Ministry said Saturday that air-launched anti-ship missiles generally don't have precision accuracy against ground targets. It said Russia likely was using such missiles because of a shortage of more accurate weapons.

The Kremlin has repeatedly claimed that the Russian military is targeting fuel storage sites and military facilities, not residential areas, although missiles also recently hit an apartment building in Kyiv and a shopping mall in the central city of Kremenchuk.

On Saturday, Kremenchuk Mayor Vitaliy Maletskyy said the death toll in the mall attack had risen to 21 and one person was still missing.

Ukrainian authorities interpreted the missile attack in Odesa as payback for the withdrawal of Russian troops from a nearby Black Sea island with both symbolic and strategic significance in the war that started with Russia's Feb. 24 invasion of Ukraine.

Moscow portrayed their departure from Snake Island as a “goodwill gesture” to help unblock exports of grain.