KYIV, May 11 - Ukraine’s top prosecutor disclosed plans Wednesday for the first war crimes trial of a captured Russian soldier, as fighting raged in the east and south and the Kremlin left open the possibility of annexing a corner of the country it seized early in the invasion.

Prosecutor General Iryna Venediktova said her office charged Sgt. Vadim Shyshimarin, 21, in the killing of an unarmed 62-year-old civilian who was gunned down while riding a bicycle in February, four days into the war, The Associated Press reported.

Shyshimarin, who served with a tank unit, was accused of firing through a car window on the man in the northeastern village of Chupakhivka. Venediktova said the soldier could get up to 15 years in prison. She did not say when the trial would start.

Venediktova’s office has said it has been investigating more than 10,700 alleged war crimes committed by Russian forces and has identified over 600 suspects.

Many of the alleged atrocities came to light last month after Moscow’s forces aborted their bid to capture Kyiv and withdrew from around the capital, exposing mass graves and streets and yards strewn with bodies in towns such as Bucha. Residents told of killings, burnings, rape, torture and dismemberment.

Volodymyr Yavorskyy of the Center for Civil Liberties said the Ukrainian human rights group will be closely following Shyshimarin’s trial to see if it is fair. “It’s very difficult to observe all the rules, norms and neutrality of the court proceedings in wartime,” he said.

Meanwhile, a Kremlin-installed politician in the southern Kherson region, site of the first major Ukrainian city to fall in the war, said officials there want Russian President Vladimir Putin to make Kherson a “proper region” of Russia — that is, annex it.

“The city of Kherson is Russia,” Kirill Stremousov, deputy head of the Kherson regional administration appointed by Moscow, told Russia’s RIA Novosti news agency.

That raised the possibility that the Kremlin would seek to break off another piece of Ukraine as it tries to salvage an invasion gone awry. Russia annexed Ukraine’s Crimean Peninsula, which borders the Kherson region, after a disputed referendum in 2014, a move denounced as illegal and rejected by most of the international community.

Kherson, a Black Sea port of roughly 300,000, provides Crimea with access to fresh water and is seen as gateway to wider Russian control over southern Ukraine.

Kremlin spokesman Dmitry Peskov said it would be “up to the residents of the Kherson region after all to decide whether such an appeal should be made or not.” He said any move to annex territory would have to be closely evaluated by legal experts to make sure it is “absolutely legitimate, as it was with Crimea.”

Ukrainian presidential adviser Mykhailo Podolyak mocked the notion of Kherson’s annexation, tweeting: “The invaders may ask to join even Mars or Jupiter. The Ukrainian army will liberate Kherson, no matter what games with words they play.”

Inside Kherson, people have taken to the streets to decry the Russian occupation. But a teacher who gave only her first name, Olga, for fear of Russian retaliation said such protests are impossible now because Moscow’s troops “kidnapped activists and citizens simply for wearing Ukrainian colors or ribbons.” She said “people are scared of talking openly outside their homes” and “everyone walks on the street quickly.”

All people in Kherson are waiting for our troops to come as soon as possible,” she added. “Nobody wants to live in Russia or join Russia.” (ap/ez)