KYIV, Ukraine (AP) — Russia said Monday that it destroyed air defence systems in Ukraine over the weekend, in what appeared to be a renewed push to gain air superiority and take out weapons Kyiv has described as crucial ahead of a broad new offensive in the east.

Moscow’s initial invasion stalled on several fronts as it met with stiff resistance from Ukrainian forces, who prevented the Russians from taking the capital and other cities. The failure to win full control of Ukraine’s skies has hampered Moscow’s ability to provide air cover for troops on the ground, limiting their advances and likely exposing them to greater losses.

Russian Defence Ministry spokesman Major General Igor Konashenkov said the military used cruise missiles to destroy four S-300 air defence missile launchers on the southern outskirts of the central city of Dnipro. He said about 25 Ukrainian troops were also hit by Sunday’s strike.

Konashenkov said Ukraine had received the air defence systems from a European country that he didn’t name. Last week, Slovakia said it handed over Soviet-designed S-300s to Ukraine — but Slovakia said it had no evidence that its system was hit.

With their advance in many parts of the country thwarted, Russian forces have relied increasingly on bombarding cities. The war has flattened many urban areas, killed thousands of people and left Russia politically and economically isolated. Ukrainian authorities accuse Russian forces of committing war crimes against civilians, including a massacre outside Kyiv, airstrikes on hospitals and a missile attack that killed at least 57 people at a train station.

Now, Russia is regrouping for a renewed push in the eastern Donbas region, where Moscow-backed separatists have been battling Ukrainian forces since 2014 and have declared independent states. Both sides are digging in for what could be a devastating war of attrition.

Russia has appointed a seasoned general to lead the effort, according to United States (US) officials, though they do not see one man making a difference.

Ukrainian President Volodymyr Zelenskyy is meanwhile pleading for more Western aid, saying his forces need heavier firepower to resist the coming onslaught and push Russian forces back. Echoing his remarks in an AP interview, Zelenskyy said Sunday that the coming week could be crucial, with Western support to his country — or the lack thereof — proving decisive.

“To be honest, whether we will be able to (survive) depends on this,” Zelenskyy said in a “60 Minutes” interview. “Unfortunately, I don’t have the confidence that we will be receiving everything we need.”

Zelenskyy said he was grateful to US President Joe Biden and other Western leaders for military aid to date but said he had “long ago” forwarded a list of specific items Ukraine desperately needs. In a video address to South Korean lawmakers on Monday, he specifically requested equipment that can shoot down Russian missiles.

Those armaments could increasingly come under attack as Russia looks to shift the balance in the 6-week-old war.

The Russian report of the attack on the S-300s outside Dnipro was the third such strike since the weekend. Konashenkov said the military also hit such systems in the Mykolaiv and Kharkiv regions. The Russian military claims couldn’t be independently verified.

Asked about the Russian claim that it had taken out systems supplied by a European country, Slovakian Foreign Minister Ivan Korcok said Monday he had “no evidence” that the Russians had destroyed the weaponry his country provided. Earlier, his government called reports that the Slovak-supplied system had been hit “disinformation.”

Ukraine already had a number of Soviet-built S-300s and other long-range air defence systems, and it also has received batches of portable, shoulder-fired Western anti-aircraft weapons like Stingers, which are efficient against low-flying aircraft.

Austrian Chancellor Karl Nehammer was due to meet Monday in Moscow with Russian President Vladimir Putin, after meeting with Zelenskyy in Kyiv. Austria, a member of the European Union, is militarily neutral and not a member of NATO.

Questions remain about the ability of depleted and demoralised Russian forces to conquer much ground after their advance on Kyiv was repelled by determined Ukrainian defenders.

Britain’s Defence Ministry said Monday that Ukraine has already beaten back several assaults by Russian forces in the eastern Donetsk and Luhansk regions — which make up the Donbas — resulting in the destruction of Russian tanks, vehicles and artillery.

In Washington, a senior US official said Russia has appointed Gen. Alexander Dvornikov, one of its most experienced military chiefs, to oversee the invasion. The official was not authorised to be identified and spoke on condition of anonymity. Russia does not generally announce such appointments, and there was no comment from Moscow.

Dvornikov, 60, gained a reputation for brutality as head of Russian forces deployed to Syria in 2015 to back President Bashar Assad’s government during the country’s devastating civil war.

Until now, Russia has had no central war commander on the ground. But US national security adviser Jake Sullivan, speaking Sunday on CNN’s “State of the Union,” played down the appointment’s significance.

“What we have learned in the first several weeks of this war is that Ukraine will never be subjected to Russia,” Sullivan said. “It doesn’t matter which general President Putin tries to appoint.”

Western military analysts say Russia’s assault increasingly is focusing on eastern Ukraine — an arc stretching from Kharkiv, Ukraine’s second-largest city, in the north, to Kherson in the south.

On Sunday, Russian forces shelled government-controlled Kharkiv and sent reinforcements toward Izyum to the southeast to try to break Ukraine’s defences, the Ukrainian military said. The Russians also kept up their siege of Mariupol, a key southern port in the Donbas that has been besieged since nearly the start of the war.

Oleh Synyehubov, the regional governor of Kharkiv, said Monday that Russian shelling had killed 11 people over the last 24 hours, including a 7-year-old child.

The Institute for the Study of War, an American think tank, predicted that Russian forces will “renew offensive operations in the coming days” from Izyum in the campaign to conquer the Donbas, which comprises Ukraine’s industrial heartland.

But it said the outcome “remains very much in question.”

In Mariupol, Russia deployed Chechen fighters, reputed to be particularly fierce. Capturing the city on the Sea of Azov would give Russia a land bridge to the Crimean Peninsula, which Russia seized from Ukraine and annexed eight years ago.

In a video posted on his Telegram channel, Chechen Leader Ramzan Kadyrov said Russian forces would launch a renewed offensive on Mariupol as well as Kyiv and other cities. “Our offensive work will be not only in Mariupol, but in all the other settlements, cities and villages,” he said.

Mariupol’s residents have lacked food, water and electricity since Russian forces surrounded the city. Hundreds of thousands have fled, though Russian attacks have also frustrated evacuation missions.

Vladislav Usovich, an 18-year-old conscript serving in Russia-backed separatist forces, advanced slowly with other fighters through residential areas around a factory in Mariupol on Sunday.

“I thought it would go better, I thought it would be faster. Everything is going slowly,” he said. “The Ukrainians are prepared fighters. NATO trained them well.”