Ukraine and Russia have accused each other of risking nuclear disaster by shelling the Zaporizhzhya nuclear power plant, which the United Nations says should have a demilitarized zone declared around it.

Western countries have called for Moscow to withdraw its troops from the plant, but there has been no sign so far of Russia agreeing to move its troops out.

"The facility must not be used as part of any military operation. Instead, urgent agreement is needed at a technical level on a safe perimeter of demilitarization to ensure the safety of the area," UN Secretary-General Antonio Guterres said in a statement.

EU foreign policy chief Josep Borrell also weighed in on the situation, echoing Guterres in saying the power plant must not be used as part of any military operation.

"I support call for demilitarisation of area starting with full withdrawal of Russian forces, and urge the @iaeaorg to visit," he said on Twitter, referring to the International Atomic Energy Agency (IAEA).

"Russia must immediately hand back full control to rightful sovereign owner Ukraine," he said.

Ukraine's Enerhotam agency said the Zaporizhzhya complex in south-central Ukraine was struck five times on August 11, including near where radioactive materials are stored. The governor of the Zaporizhzhya region said the plant was hit again on the evening of August 12.

Russian-appointed officials, meanwhile, accused Ukraine of shelling the plant twice, disrupting a shift changeover, the state-run TASS news agency said.

Vladimir Rogov, a member of the Moscow-installed regional administration, said on August 12 that Ukraine's strikes may lead to an emergency reactor shutdown.

The Ukrainian military denies having struck the plant, saying Russian troops struck it themselves and are using it as a shield to provide cover while they bombard nearby towns and cities.

Shelling overnight of one of those towns, Marhanets, injured three civilians, said Valentyn Reznichenko, governor of the Dnipropetrovsk region.

Ukrainian forces control Marhanets and other towns and cities on the opposite bank of the Dnieper River, and they have come under intense bombardment from the Russian-held side in recent days.

A UN Security Council meeting on August 11 discussed the situation, and Guterres called on both sides to stop all fighting near the plant.

The United States backed the call for a demilitarized zone and urged the International Atomic Energy Agency (IAEA) to visit the site.

Russia's ambassador to the UN, Vasily Nebenzya, said IAEA officials could visit the site as soon as this month.

Speaking at the Security Council meeting, he said the world was being pushed "to the brink of nuclear catastrophe" comparable in scale with the 1986 Chornobyl disaster.

Ukrainian UN Ambassador Serhiy Kyslytsya accused Russia of using "elaborate plans of deceit, sabotage, and cover-ups" to stage the shelling, which he said poses "an unprecedented threat to nuclear security for Ukraine, to Europe, and the world as a whole."

The Ukrainian military’s General Staff, meanwhile, on August 12 reported widespread shelling and air attacks by Russian forces on scores of towns and military bases, especially in the east where Russia is trying to expand territory held on behalf of separatist proxies.

Other parts of the main front line have been comparatively static in recent weeks, but fighting has been intensifying in anticipation of a planned counteroffensive in the south.

In the province of Mykolayiv, the governor’s press officer said the region is still experiencing shelling, but it has become "a little quieter."

Dmytro Pletenchuk, the press officer of the Mykolayiv military administration, said this is because there is currently a shortage of ammunition in the Russian military.

Ukrainian forces have hit Russian ammunition warehouses, and the Russian forces have now switched to more outdated weapons systems, he said on Ukrainian television.

"Now the situation has changed. There is a shortage of ammunition among the Russians. And that is very good. We feel the result of the work on their warehouses -- it has become a little quieter in Mykolayiv, but the region is being shelled," he said.

Elsewhere on the battlefield, shelling killed two civilians and wounded 13 others in Kramatorsk, the last major city under Ukrainian control in the eastern Donetsk region.

Pavlo Kyrylenko, governor of the eastern Donetsk region, said on Facebook the bombardment damaged at least 20 buildings and caused a fire to break out. He called for remaining residents to evacuate.

With reporting by RFE/RL's Ukrainian Service, AP, and Reuters