Ukrainian President Volodymyr Zelenskyy has warned that any talks with Russia will be impossible if a trial of captured Ukrainian soldiers goes ahead.
Meanwhile, Russian forces pressed on with their offensive across several Ukrainian regions on Monday. Artillery shells rained down on Nikopol, a city near Europe's biggest nuclear plant at Zaporizhzhia, while missiles struck near the Black Sea port of Odesa over the weekend.
In his nightly address on Sunday, the Ukrainian president warned that in Mariupol the ground was being prepared for "an absolutely disgusting and absurd show trial".
"This will be the line beyond which any negotiations are impossible," Zelenskyy said, accusing Moscow of violating international rules.
The president believes a trial is being prepared to coincide with Ukraine's Independence Day on Wednesday, which also marks six months since the Russian invasion. At the weekend he called for vigilance, saying Moscow could try "something particularly ugly".
In May, the Ukrainian Azov regiment entrenched in the Azovstal steel plant in Mariupol was ordered by Kyiv to surrender to Russian forces. The Ukrainian authorities said this was the only way to save the lives of Mariupol defenders who spent months besieged in the plant under constant shelling, with no access to basic supplies.
Zelenskyy said at the weekend that he had discussed "all the threats" with French President Emmanuel Macron, and word had also been sent to other leaders including Turkish President Tayyip Erdogan and UN Secretary General Antonio Guterres.
"All of Ukraine's partners have been informed about what the terrorist state (Russia) can prepare for this week," the president said.
Turkey's Erdogan has reportedly dismissed speculation about
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