SIVERSK, Ukraine: The Ukrainian army retreated from the strategic city of Lysychansk over the weekend, allowing Russia to seize control of its pro-West neighbor’s entire eastern Luhansk region and claim a major victory.

The withdrawal followed weeks of fierce fighting and marked a decisive breakthrough for Moscow’s forces more than four months after their invasion and after turning their focus away from the capital Kyiv.

The retreat came as leaders from dozens of countries and international organizations were to meet in Switzerland on Monday to map out a “Marshall Plan” to rebuild Ukraine, which they aim to begin even as Russia’s offensive continues.

A major flashpoint in the conflict, Lysychansk had been the final holdout in the Luhansk area of Ukraine’s eastern Donbas region, and Moscow’s capture of it allows its forces to advance toward Kramatorsk and Sloviansk in the neighboring Donetsk region.

“The continuation of the defense of the city would lead to fatal consequences” in the face of Russia’s superiority in numbers and equipment, the Ukrainian army said in a statement announcing its retreat on Sunday night.

“In order to preserve the lives of Ukrainian defenders, a decision was made to withdraw,” it added. “Unfortunately, steel will and patriotism are not enough for success. Material and technical resources are needed.”

The fall of Lysychansk comes after Russian forces seized its twin city of Sievierodonetsk last week after intense fighting.

In his Sunday night address, Ukrainian President Volodymyr Zelenskyy vowed that Kyiv would fight on and ensure that the military had “the most modern weapons.”

“Ukraine will reach the level when the fire superiority of the occupiers will be leveled,” he said.

The latest country to provide aid was Australia, whose premier Anthony Albanese on Sunday pledged additional military support, including armored vehicles and drones, during a meeting with Zelenskyy in Kyiv.

Also on Sunday, Moscow accused Kyiv of firing three cluster missiles at the Russian city of Belgorod near the Ukrainian border, which came a day after neighboring Belarus said it had intercepted Ukrainian missiles.

In what would represent an escalation of the conflict, Russia said its anti-aircraft defenses shot down three Tochka-U cluster missiles launched by “Ukrainian nationalists” against Belgorod.

Eleven residential buildings and 39 houses were damaged, Belgorod Gov. Vyacheslav Gladkov said.

Moscow previously accused Kyiv of launching strikes on Russian soil, particularly in the Belgorod region.

Belarus slams Ukraine

On Saturday, Belarusian leader Alexander Lukashenko accused Kyiv of provocation and said his army intercepted missiles fired at his country by Ukrainian forces about “three days ago.”

Belarus, a Russian ally, supported the February 24 invasion and has been accused by Kyiv of launching its own attacks on Ukrainian territory.

Lukashenko denied any involvement in a recent cross-border incident, saying Belarus did “not intend to fight in Ukraine.”

About 75 kilometers (45 miles) west of Lysychansk, the city of Sloviansk saw heavy Russian shelling that left six people dead, including a nine-year-old girl, Zelenskyy said on Sunday night.

About 20 others were wounded as “the Russian army once again brutally shelled” the city, as well as Kramatorsk and Kharkiv, he added.

A strike on the town of Dobropillia, just southwest of Sloviansk, killed two people and wounded three, including two children, Donetsk authorities said.

The city of Siversk, 30 kilometers west of Lysychansk, also saw overnight shelling, residents and an official told Agence FrancePresse (AFP).

According to the Ukrainian parliament, the number of children who died as a result of Russia’s armed aggression reached 345 as of Monday.

Also on Monday, leaders from dozens of countries and international groups were set to gather in the Swiss city of Lugano, where they aim to hash out a road map for Ukraine’s reconstruction, which is expected to cost hundreds of billions of dollars.

Ukraine will also face demands for broad reforms, especially in cracking down on corruption after Brussels recently granted Kyiv candidate status in its push to join the 27-member European Union.

British Foreign Secretary Liz Truss is due to pledge both immediate humanitarian assistance and access to British financial and economic expertise, the United Kingdom’s foreign office said.

She will tell delegates that Ukraine’s recovery “will be a symbol of the power of democracy over autocracy,” it added.

But for residents in Bucha, a Ukrainian town synonymous with war crimes blamed on Moscow’s forces after their retreat in April, fear remains even as talk begins of reconstruction.

“We’re going to bed without knowing if we’ll wake up tomorrow,” said Vera Semeniouk, 65.

“Everyone has come back [and] starting to repair houses. Many are putting in new windows. It would be terrible if it started again and we had to leave everything again,” she added.