Russian forces fired cruise missiles at the southern Ukrainian city of Odesa on Saturday and bombarded a besieged steel mill in Mariupol, hoping to complete their conquest of the port in time for Victory Day celebrations. Officials announced that the last women, children and older adults had been evacuated from the mill, but Ukrainian fighters remained trapped.

In a sign of the unexpectedly effective defense that has sustained the fighting into its 11th week, Ukraine’s military flattened Russian positions on a Black Sea island that was captured in the war’s first days and has become a symbol of resistance.

Western military analysts also said a Ukrainian counteroffensive was advancing around the country’s second-largest city, Kharkiv, even as it remained a key target of Russian shelling.

The largest European conflict since World War II has developed into a punishing war of attrition that has killed thousands of people, forced millions to flee their homes and destroyed large swaths of some cities. Ukrainian leaders warned that attacks would only worsen in the lead-up to Russia’s holiday on Monday celebrating Nazi Germany’s defeat 77 years ago, and President Volodymyr Zelenskyy urged people to heed air raid warnings.

U.S. Secretary of State Antony Blinken said Saturday that Zelenskyy and his people “embody the spirit of those who prevailed during the Second World War.” He accused Russian President Vladimir Putin of trying “to twist history to attempt to justify his unprovoked and brutal war against Ukraine.”

“As war again rages in Europe, we must increase our resolve to resist those who now seek to manipulate historical memory in order to advance their own ambitions,” Blinken said in a statement as the United States and United Kingdom commemorated the Allied victory in Europe.

The most intense fighting in recent days has been in eastern Ukraine, where the two sides are entrenched in a fierce battle to capture or reclaim territory. Moscow’s offensive there has focused on the Donbas, where Russia-backed separatists have been fighting since 2014.

The governor of the Luhansk region, one of two that make up the Donbas, said a Russian strike destroyed a school in the village of Bilogorivka where 90 people were seeking safety in the basement. Gov. Serhiy Haidai, who posted pictures of the burning rubble on Telegram, said 30 people were rescued. The emergency services later reported that two bodies had been found and more could still be buried under the rubble. Rescue work was suspended overnight but was to resume on Sunday.

Haidai also said two boys aged 11 and 14 were killed by Russian shelling in the town of Pryvillia, while two girls aged 8 and 12 and a 69-year-old woman were wounded.

Moscow also has sought to sweep across southern Ukraine both to cut off the country from the sea and create a corridor to the breakaway Moldovan region of Transnistria, long home to Russian troops. But it has struggled to achieve those objectives.

On Saturday, six Russian cruise missiles fired from aircraft hit Odesa, where a curfew is in place until Tuesday morning. Videos posted on social media showed thick black smoke rising over the Black Sea port city as sirens wailed.

The Odesa city council said four of the missiles hit a furniture company, with the shock waves and debris badly damaging high-rise apartment buildings. The other two missiles hit the Odesa airport, where the runway had already been taken out in a previous Russian attack.

Air raid sirens sounded several times early Sunday, the city council said.

Satellite photos analyzed by The Associated Press showed Ukraine targeting Russian-held Snake Island in a bid to impede Russia’s efforts to control the Black Sea. An image taken early Saturday by Planet Labs PBC showed that most of the island’s buildings had been destroyed by Ukrainian drone attacks, as well as what appeared to be a Serna-class landing craft against the island’s northern beach.

The image corresponds with a Ukrainian military video showing a drone striking the Russian vessel, engulfing it in flames. Snake Island, located some 35 kilometers (20 miles) off the coast, figured in a memorable incident early in the war when Ukrainian border guards stationed there defied Russian orders to surrender, purportedly using colorful language.

In Mariupol, Ukrainian fighters made a final stand against a complete Russian takeover of the strategically important city, which would give Moscow a land bridge to the Crimean Peninsula, annexed from Ukraine during a 2014 invasion.

Satellite photos shot Friday by Planet Labs PBC showed vast devastation at the sprawling Azovstal seaside steel mill, the last pocket of Ukrainian resistance in the city. Buildings had gaping holes in the roofs, including one under which hundreds of fighters were likely hiding.

After rescuers evacuated the last civilians Saturday, Zelenskyy said in his nightly address that the focus would turn to extracting the wounded and medics: “Of course, if everyone fulfills the agreements. Of course, if there are no lies.”

He added that work would also continue Sunday on securing humanitarian corridors for residents of Mariupol and surrounding towns to leave.

The situation at the plant has drawn the world’s attention, with the United Nations and the International Committee of the Red Cross desperately trying to organize evacuations.

In recent days, fighters inside described bringing out small groups of civilians who had been hiding there for weeks. The fighters said via social media that both they and the Russians had used a white flag system to halt fighting in order to get civilians out.

But Russian forces have intensified fire on the mill with mortars, artillery, truck-mounted rocket systems, aerial bombardment and shelling from the sea, making evacuation operations difficult.

Three Ukrainian fighters were reportedly killed and six more wounded during an evacuation attempt Friday. Capt. Sviatoslav Palamar, the deputy commander of the Azov Regiment, said his troops had waved white flags, and he accused Russian forces of firing an anti-tank weapon at a vehicle.

It remains unclear what will happen to the estimated 2,000 fighters at Azovstal, both those still in combat and the hundreds believed to be wounded. In recent days the Ukrainian government has been reaching out to international organizations to try to secure safe passage for them. The fighters have repeatedly vowed not to surrender.

Zelenskyy said officials were trying to find a way to evacuate them. He acknowledged the difficulty, but said: “We are not losing hope, we are not stopping. Every day we are looking for some diplomatic option that might work.”

Russian forces have probed the plant and even reached into its warren of tunnels, according to Ukrainian officials.

Kharkiv, which was the first Soviet capital in Ukraine and had a prewar population of about 4 million, remained a key target of Russian shelling in the northeast. Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said Saturday that the Russian military also hit large shipments of weapons from the U.S. and other Western countries with Iskander missiles in the region. His claims couldn’t be independently verified.

But Western military analysts said Ukrainian forces were making progress in securing positions around the city. The Ukrainian military said it retook control of five villages and part of a sixth, and that Russian forces destroyed three bridges on a road northeast of the city to try to slow Ukraine’s advance.

A Washington-based think tank, the Institute for the Study of War, said in its most recent assessment that Ukraine may be able to push Russian forces “out of artillery range of Kharkiv in the coming days,” providing a respite for the city and an opportunity to build the defenders’ momentum “into a successful, broader counteroffensive.”

Overnight, a Russian missile destroyed a national museum in the Kharkiv region dedicated to the life and work of 18th-century philosopher and poet Gregory Skovoroda, the local council said. It posted photographs on Facebook showing the building engulfed in flames.

Zelenskyy expressed outrage at the missile attacks on the museum and on Odesa, “where almost every street has something memorable, something historical.” He said Russian forces have destroyed or damaged about 200 cultural heritage sites.

“Every day of this war, the Russian army does something that leaves you speechless,” he said. “But then the next day it does something that makes you feel this way in a new way.”