KYIV — Ukrainian President Volodymyr Zelensky 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," Zelensky 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 violent".

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 potential talks between Zelensky and Vladimir Putin. After speaking to his Russian counterpart, Macron said Russia accused Russia of having launched a "brutal attack" on Ukraine in an imperialist, revanchist violation of international law.

In Russia, authorities are investigating a suspected car bomb attack outside Moscow that killed Daria Dugina — the daughter of Alexander Dugin, an ultra-nationalist Russian ideologue who advocates Russia absorbing Ukraine.

While investigators said they were considering "all versions" when it came to establishing who was responsible, the Russian Foreign Ministry speculated there could be a link to Ukraine.

Kyiv has dismissed the accusation. "Ukraine, of course, had nothing to do with this because we are not a criminal state, like the Russian Federation, and moreover we are not a terrorist state," Mykhaylo Podolyak said on Ukrainian TV.

Meanwhile, Ukrainian officials reported more Russian strikes on targets in the east and south of the country.

In the eastern Bakhmut region, Russian forces inflicted damage from artillery and multiple rocket launcher systems in the areas of Soledar, Zaytseve and Bilogorivka settlements, Ukraine's General Staff said in its daily update on Monday.

They continued to focus their efforts on establishing full control over the territories of Luhansk and Donetsk regions, maintaining the captured areas of Kherson and parts of Kharkiv, Zaporizhzhia, and Mykolaiv regions, the General Staff added.

Nikopol was shelled on five different occasions overnight, regional governor Valentyn Reznichenko wrote on Telegram on Sunday. He said 25 artillery shells hit the city, causing a fire at an industrial premises and cutting power to 3,000 residents.

The fighting near Zaporizhzhia and a missile strike on the southern town of Voznesensk, not far from Ukraine's second-largest atomic plant, have spurred fears of a nuclear accident.

On Sunday, US President Joe Biden, British Prime Minister Boris Johnson, German Chancellor Olaf Scholz and Macron held a phone call stressing the importance of ensuring the safety of nuclear installations, while underlining their "steadfast commitment" to Ukraine.

Russia said on Sunday that its Kalibr missiles had destroyed an ammunition depot containing missiles for US-made HIMARS rockets in Ukraine's southeastern Odesa region, home to ports critical to a UN-brokered plan to help Ukrainian agricultural exports reach world markets again.

Kyiv said a granary had been hit.

The battlefield claims have not been independently verified. — Euronews