President Volodymyr Zelensky warned overnight that the fate of Ukraine’s entire Donbas region is dependent on the strategic city of Severodonetsk, as he urged defenders to push back against Russian advances that have dimmed the outlook for his embattled country’s eastern region.

The war in Ukraine, which entered its 16th week on Thursday, has shifted decisively from attempts to capture Kyiv and the northeastern metropolis of Kharkiv to the eastern industrial heartland, where Russia has long fomented separatism and now controls large swaths of territory.

As embassies reopen, Kyiv, where missiles hit suburbs and mass graves were discovered earlier in the war, is welcoming back foreign dignitaries, and Russian forces have been largely repelled around Kharkiv. However, Moscow’s troops have taken over the southeastern port city of Mariupol, where Ukrainian fighters resisted for weeks in an underground steelworks complex under sustained attack, and Kherson, the southern coastal city that was the first to fall.

Now, in one of the few areas where Kiev and Moscow appear to agree, the Donbas appears poised to fall unless Ukrainians stage a turnaround — something they have done before in other parts of this fertile land, but which is becoming increasingly difficult.

Severodonetsk in Luhansk, one of the two provinces that comprise the Donbas, is the “epitome of the conflict,” Zelensky said in an overnight address Wednesday. He claimed that Ukraine had caused “significant losses to the enemy.” However, that claim could not be verified and came just days after Russian Defense Minister Sergei Shoigu claimed that Russia had “liberated” 97 percent of Luhansk, a term Moscow uses to describe the war as an effort to save Ukrainians and Russian speakers from a corrupt “neo-Nazi” government.

“The fate of our Donbas is being decided there,” Zelensky said of Severodonetsk, where the two sides have been fighting in the streets. Severodonetsk and its sister city, Lysychansk, both on the strategic Seversky Donets River, have previously been described as “dead cities” ravaged by the grinding war of attrition.

The air was filled with booms, the whoosh of rocket launchers releasing their payloads, and the ripping sound of heavy machine guns. The hours-long artillery battles between Ukrainians and their Russian opponents had left much of Severodonetsk on fire Thursday morning.

Even as fighting engulfed parts of Lysychansk, some residents refused to leave.

However, Serhiy Haidai, the regional governor of Luhansk, stated in a statement that the situation was so dire that evacuations from the city were impossible. Intermittent evacuations continued in other hard-hit cities, including Mariupol on the Sea of Azov, even as battles for territorial control raged.

Haidai, like Zelensky, stated that Ukraine required more long-range weapons from the West to help with defenses. Ukraine could retake positions in Severodonetsk “in two or three days” with those, according to the governor.

Taking over the Donbass would allow Moscow to fulfill its ambitions of expanding its territorial control westward, adding to the territory it has already taken from Ukraine. This includes Crimea, the peninsula it annexed illegally in 2014.

The Donbas is also home to a significant portion of Ukraine’s agricultural industry. The country, known as the “breadbasket of Europe,” has seen its exports thwarted by Russian ships stationed at its ports. The majority of exports are typically destined for North Africa and the Middle East.

On Thursday, Zelensky warned of a potential food crisis if foreign countries and humanitarian organizations do not intervene to help free up corn, oil, and wheat exports.

Zelensky warned that the world was on the verge of a “terrible food crisis,” a view shared by humanitarian and trade organizations in recent months.

Turkey, which previously hosted the two sides’ talks, has been attempting to coordinate an agreement between Kyiv and Moscow to allow grain shipments across the Black Sea.

Ukraine has accused Russia of using the war to steal grain from its lands, an accusation that has been called into question by the British Foreign Secretary, among others.

Dmitry Peskov, a Kremlin spokesman, told reporters Thursday that no agreement on grain exports had been reached and that talks were ongoing.