He said civilians will have to be dug from bunkers under a steel mill, the last stronghold of the resistance in Mariupol, Ukraine.

Unable to capture the capital, Kiev, in the first weeks of the occupation, which killed thousands and destroyed towns and villages, Russia stepped up its attacks in the south and east of Ukraine, including the Azovstal steelworks in Mariupol.

Ukraine’s resistance at the factory underscores Russia’s failure to seize major cities in a war that unites Western powers by arming Kiev and punishing Moscow with sanctions. Sweden and Finland are expected to decide very soon whether to join the North Atlantic Treaty Organization (NATO) western military alliance, which will be a major historic change.

The Russian military has pledged to halt its activities in Azovstal to allow civilians to leave on Thursday and for the next two days, after Ukrainian fighters blocked a retreat Wednesday described as “bloody battles”. The Kremlin said the steel mill’s humanitarian corridors were working.

Ukrainian officials believe that around 200 civilians, along with fighters, are trapped in the sprawling network of underground bunkers at the Soviet-era Azovstal complex.

In an early morning speech, Zelensky said Ukraine was ready to reach a ceasefire in Mariupol, a Russian-controlled port city after a weeks-long siege, excluding the steel mill.

“It will only take time to get people out of these basements, these underground bunkers. Under the current conditions, we cannot use heavy equipment to remove the rubble. Everything has to be done by hand,” Zelensky said.

Ukraine’s Azov regiment commander Denis Prokopenko said late Wednesday that Ukrainian fighters inside Azovstal are waging “hard and bloody battles”.

Ukraine’s military personnel said the attack on the steel mill involved air support, and photos released by Russian-backed fighters showed the smoke and flames enveloping it.

Tetyana Trotsak, who was evacuated from Azovstal among dozens of people who arrived in a Ukrainian-held town this week, described her two-and-a-half-hour walk and said, “God forbid that more shells come to civilian shelters.” along a short piece of land covered with factory rubble.

Mariupol is a key target in Russia’s efforts to cut Ukraine off grain and metal export routes in the Black Sea and connect the Russian-controlled region in the east of the country with Crimea, which Moscow took over in 2014.

The United Nations and the Red Cross have evacuated hundreds of people from the city and other areas this week.

The UN humanitarian office said on Wednesday that no one from Azovstal was among the more than 300 civilians evacuated from Mariupol and other areas in southern Ukraine.

Office spokesman Jens Laerke said in an email that “we are ready to assist” the detained civilians.