A Russian ultimatum for the last remaining Ukrainian forces in Mariupol to surrender expired on Sunday, with Moscow poised for a major strategic victory in the southeastern port city. Ukraine has vowed to "fight to the end" in the besieged city. 

"The city still has not fallen," Ukrainian Prime Minister Denys Shmyhal told ABC's "This Week" hours after the Russian ultimatum had expired, adding that the encircled soldiers will "fight to the end." 

Russian forces claim to have brought Mariupol under their control, though some Ukrainian fighters remain holed up in the city's fortress-like steelworks. Ukraine had warned that an "elimination" of them would put an end to any negotiations with Russia. Ukrainian Deputy Prime Minister Iryna Vereshchuk had urged Russian forces to allow evacuations from Mariupol. 

In Kyiv, renewed Russian air strikes hit an armaments factory on Sunday, despite Moscow shifting its military focus to gaining control of the eastern Donbas region and forging a land corridor to Crimea.  

"During the night, high-precision, air-launched missiles destroyed an ammunitions factory near the settlement of Brovary, Kyiv region," Russia's Defense Ministry said, the third such air strike near the capital in as many days.

Moscow on Saturday had issued an ultimatum to the remaining Ukrainian fighters in Mariupol, urging them to lay down their arms by 6:00 a.m. Moscow time (0300 GMT) and to evacuate before 1:00 p.m.

"Taking into account the catastrophic situation that has developed at the Azovstal metallurgical plant, as well as being guided by purely humane principles, the Russian Armed Forces offer the militants of nationalist battalions and foreign mercenaries from 06:00 on April 17, 2022, to stop any hostilities and lay down their arms," the Russian Defense Ministry said in a statement.

"All who lay down their arms are guaranteed that their lives will be spared," it said, adding that the defenders could leave the plant by 10 a.m. without arms or ammunition.

Ukrainian President Volodymyr Zelenskyy warned on Saturday that eliminating Ukrainian troops in Mariupol would put an end to any negotiations with Russia.

"The elimination of our troops, of our men (in Mariupol) will put an end to any negotiations" between Ukraine and Russia, Zelenskyy said in an interview. "That will be an impasse as we don't negotiate neither our territories nor our people."

Zelenskyy said Ukraine is ready to discuss refusing NATO membership and the status of Crimea with Russia but only after its troops are withdrawn from Ukrainian territory.

The Ukrainian Defense Ministry said Friday that its forces were still fighting against Russians in Mariupol after almost seven weeks since the city was besieged.

As a key port city on the Azov Sea, Mariupol is witnessing one of the worst violence since the start of the Russia-Ukraine conflict on February 24.

Its capture would allow Russia to connect the Crimean peninsula, which it took over in 2014, to the pro-Moscow breakaway regions in Ukraine's east by land.

Read more:

Timeline: The battle for Mariupol

CGTN correspondent Dmitriy Maslak visits Mariupol

(With input from agencies)