Ukraine’s military said it was inflicting heavy losses on Russian forces in the south of the country in an area that military analysts suggest could be the next target for a Ukrainian offensive.

The General Staff of the Ukrainian Armed Forces said that the losses had forced Russian troops to set up a field hospital at a hotel complex in the city of Berdyansk. 

Ukrainian reporters posted footage of what they said was a Ukrainian strike on a Russian headquarters in Tokmak, a Russian-occupied transport hub.

And the Ukrainian mayor of Melitopol, a Russian-occupied city, said eyewitnesses had reported a large explosion there that appeared to have damaged a vehicle used by Russian forces. He said there was no information on the occupants of the vehicle, but partisans have carried out several attacks in the area that have targeted senior collaborators.

After recapturing swaths of territory around the northeastern city of Kharkiv and the southern city of Kherson, Ukrainian forces are seeking to maintain momentum. In recent weeks, they have carried out strikes on Russian military facilities and transport infrastructure in the south of the country, in what analysts say could be a preparatory phase for a thrust south toward the Black Sea. A Ukrainian advance there would cut critical lines of supply between Russia and Crimea, the Ukrainian peninsula that Russia has occupied since 2014.

A prosecutor walks among collected parts of Russian rockets used to attack the Ukrainian city of Kharkiv.

Photo: Evgeniy Maloletka/Associated Press

Russia has begun taking defensive measures in Crimea, most recently starting engineering work on defensive positions along a highway that spans the top of the peninsula where it meets mainland Ukraine.

Meanwhile, Kremlin spokesman Dmitry Peskov told reporters Friday that Russian forces had made significant progress toward Moscow’s stated, but undefined, goal of demilitarizing Ukraine. He said that while any conflict ends at the negotiating table, there are currently no contacts between Washington and Moscow on how to end the war and that the Kremlin isn’t in the loop on a reported Ukrainian peace plan. 

During his whirlwind trip to Washington this week, Ukrainian President Volodymyr Zelensky told Congress that Kyiv was developing a peace formula, following recent discussions by Ukrainian officials of a 10-point plan. Mr. Zelensky’s team is currently fleshing out the plan and aims to present its ideas on or around the first anniversary of Russia’s Feb. 24 invasion, according to European and Ukrainian diplomats.

Russian Defense Minister Sergei Shoigu, meanwhile, visited Russian arms manufacturer the Kalashnikov Group’s plant in the city of Izhevsk in central Russia on Friday. A video released by the Defense Ministry showed Mr. Shoigu inspecting what it said were Kalashnikov’s assault and sniper rifles, precision-guided munitions and portable air-defense systems, and telling the company’s general director that the plant’s state contracts would be significantly increased next year. 

Write to James Marson at james.marson@wsj.com and Evan Gershkovich at evan.gershkovich@wsj.com