ODESA and LVIV, Ukraine — Ukraine emphatically rejected Russia's calls to surrender the strategic southern port city of Mariupol, which Russian forces have besieged and encircled.

After weeks of bombarding the city, which is filled with civilians trapped in deteriorating conditions, Russia offered the ultimatum on Sunday: If Mariupol surrenders, it will let civilians leave and humanitarian aid enter.

Ukrainian officials have refused, in absolute terms — though Ukrainian President Volodymyr Zelenskyy told CNN that he is willing to talk to Russian President Vladimir Putin about negotiating an end to the fighting.

Hard-hit Mariupol will not surrender to Russia

Hundreds of thousands of civilians are trapped in Mariupol, which has no electricity and dwindling supplies of food and water. The city has been the site of at least two bombings of buildings where civilians were seeking shelter: a school and a theater.

Ukrainian officials have so far refused Russia's calls for surrender, with an adviser to the city's mayor even going so far as to use an expletive in a Facebook post rejecting the ultimatum. Ukraine's deputy prime minister told a newspaper that Russia's demands were eight pages of "delusions" and that Russians have taken the people of Mariupol hostage and a surrender is not on the table.

More than 41,000 people have left Mariupol in the past five days, according to its city council, with more evacuations and humanitarian corridors planned Monday.

Here's what's happening in the rest of Ukraine:

Odesa is gearing up for a fight

In Odesa, the feeling in the air, in a word, is defiant.

Under normal circumstances, the Black Sea port city would be drawing tourists in with its 19th century architecture and world-famous opera house and would be bustling with people headed to bars and clubs. But the streets are now blocked off by checkpoints, anti-tank hedgehogs and sandbags, guarded by men with rifles.

Odesa's mayor has cited a proverb when discussing preparations for a potential attack: If you want peace, be ready for the war. He says the city is ready for that attack. The Ukrainian military also says it's confident they'll be able to repel any assault on the Odesa region.

NPR was permitted to review some of their defenses during a trip in the last 24 hours and observed hardened fighting positions, armored vehicles and mined beaches ready to repel a Russian attempt.

Ukrainian officials are watching for potential new fronts

Elsewhere in the country, the Russian military remains stalled in the areas around Kyiv and forces still haven't taken control of any major Ukrainian cities.

Ukrainian officials are on the lookout for new fronts possibly opening, and not just in the south, where Russia's military has been seeing more success. Overnight, the governor of Rivne, a region along Ukraine's northern border with Belarus, announced it had been struck with two missiles.

There has been concern in recent weeks that Russian and even Belarusian troops might open a new front there.

The strikes in Rivne seem to indicate that the Russian military wants to keep that possibility open, or at least keep Ukrainians thinking so.

Rachel Treisman reported from Washington, D.C.

This story also appeared on the Morning Edition live blog.

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