Russian shelling killed 13 people in Ukraine's Dnipropetrovsk region overnight, Governor Valentyn Reznychenko said Wednesday, as British intelligence said Moscow had "almost certainly" organized a major new ground force to support its ongoing war.

The new Russian force, called the 3rd Army Corps, is based in the city of Mulino, east of Russia's capital, Moscow, the British Defense Ministry said in a daily intelligence bulletin.

The ministry also said Russian commanders were facing "competing operational priorities" of reinforcing their offensive in the Donbass region in the east, as well as strengthening defenses against Ukrainian counterattacks in the south.

After failing to capture the Ukrainian capital of Kyiv early in the war, Russian forces have focused on the east and south, where pro-Moscow separatists have controlled territory since Russia annexed Crimea in 2014.

A senior Ukrainian official suggested a series of explosions at a Russian air base in Crimea on Tuesday could have been the work of partisan saboteurs, as Ukraine denied responsibility for the incident deep in Russian-occupied territory.

Huge plumes of smoke could be seen in videos posted on social media from Crimea, a holiday destination for many Russians. Russia used Crimea as one of the launch pads for its Feb. 24 invasion.

Russia said the explosions, at least 12 according to witnesses, were detonations of stored ammunition, not the result of an attack.

Ukrainian President Volodymyr Zelenskyy did not directly mention the blasts in his daily video address on Tuesday but said it was right that people were focusing on Crimea.

"We will never give it up ... the Black Sea region cannot be safe while Crimea is occupied," he said, repeating his government's position that Crimea would have to be returned to Ukraine.

High risk

Ukraine's general staff reported widespread Russian shelling across several regions on Wednesday.

The head of Ukraine's state nuclear power firm has warned of the "very high" risk of shelling at the Zaporizhzhia nuclear power plant in the Russian-occupied south and said it was vital Kyiv regained control of the facility in time for winter.

Shelling last week by Russian forces had damaged three lines that connect the plant to the Ukrainian grid, he said. Russia wanted to connect the facility to its grid, Petro Kotin said.

"The risk is very high" of shelling hitting containers storing radioactive material, he said.

Ukraine on Wednesday accused Russia of exploiting its position in a nuclear power plant it had seized to target a nearby town in a rocket attack that left many others seriously wounded.

The town Ukraine says Russia targeted - Marhanets - is one that Russia has alleged Ukrainian forces have used in the past to shell Russian forces who are holed up at the Zaporizhzhia nuclear power plant which they took over in March.

Both Ukraine and Russia have said they want technicians from the U.N. nuclear watchdog, the International Atomic Energy Agency (IAEA), to visit Zaporizhzhia, the biggest nuclear power plant in Europe.

Russia has asked for IAEA chief Rafael Grossi to brief the U.N. Security Council on Thursday on Russia's accusation of attacks by "the Ukrainian armed forces on the Zaporizhzhia nuclear power plant and their potential catastrophic consequences," diplomats said.

Ukraine has denied the Russian assertion that its forces attacked the plant.

Mass burials

In the northern town of Bucha, 15 bodies were buried on Tuesday after they were found four months after Russian forces withdrew from the area.

"All the people who were shot and exhumed from a mass grave have torture marks," Bucha Deputy Mayor Mykhailyna Skoryk told reporters.

Ukraine and its allies accuse Russian forces of committing atrocities in Bucha, a satellite town of the capital Kyiv, after beginning its invasion on Feb. 24.

Russia denied the accusation and denies targeting civilians in what it calls its "special military operation" in its southern neighbor.

Ukraine and its allies say Russia is responsible for an unprovoked imperial-style war of aggression that has ignited the biggest conflict in Europe since World War II.

Supported with weapons by its Western allies, Ukraine is banking on sophisticated rocket and artillery systems to degrade Russian supply lines and logistics.

The U.S. State Department has approved $89 million worth of assistance to help Ukraine equip and train 100 teams to clear land mines and unexploded ordnance for a year.

Ukraine's president has called on the West to impose a blanket travel ban on Russians, an idea that has found support among some EU member states, but angered Russia, which dismissed it as irrational.

President Joe Biden on Tuesday signed documents of U.S. support for Finland and Sweden joining NATO, the most significant expansion of the military alliance since the 1990s and prompted by Russia's invasion of Ukraine.