UN Secretary-General Antonio Guterres called on Monday for international inspectors to be given access to the Zaporizhzhia nuclear plant after Ukraine and Russia traded accusations over the shelling of Europe's largest atomic plant at the weekend.

"Any attack (on) a nuclear plant is a suicidal thing," Guterres told a news conference in Japan, where he attended the Hiroshima Peace Memorial Ceremony on Saturday to commemorate the 77th anniversary of the world's first atomic bombing.

Russian forces captured the Zaporizhzhia nuclear reactor complex in southeastern Ukraine in early March, shortly after Moscow's invasion of its neighbour, but it is still run by Ukrainian technicians.

Ukraine accused Russia of responsibility for renewed shelling on Saturday that had damaged three radiation sensors and injured a worker at the plant in what was the second hit in consecutive days on the site.

Ukrainian President Volodymyr Zelenskiy, in a televised address on Sunday, said Russia was waging "nuclear terror" that warranted more international sanctions, this time on Moscow's nuclear sector.

The region's Russian-installed authority said Ukrainian forces hit the site with a multiple rocket launcher, damaging administrative buildings and an area near a storage facility.

The Russian Embassy in Washington also itemised the damage, saying artillery fire from "Ukrainian nationalists" damaged two high-voltage power lines and a water pipeline, but critical infrastructure was not affected.

Reuters could not verify either side's version of what happened.

Events at the Zaporizhzhia site - where Kyiv alleged that Russia hit a power line on Friday - have alarmed the world.

Guterres said the International Atomic Energy Agency (IAEA) needed access to the plant. "We fully support the IAEA in all their efforts in relation to creat(ing) the conditions for stabilisation of the plant," he said.

IAEA Director General Rafael Mariano Grossi warned on Saturday that the latest attack "underlines the very real risk of a nuclear disaster".

GRAIN EXPORTS PICK UP STEAM

Elsewhere, a deal to unblock Ukraine's food exports and ease global shortages gathered pace as two grain ships sailed out of Ukrainian Black Sea ports on Monday, raising the total to 12 since the first vessel left a week ago.

Four ships that left Ukraine on Sunday are expected to anchor near Istanbul on Monday evening, Turkey's defence ministry said, and would be inspected on Tuesday, while the first vessel to sail since Russia's Feb. 24 invasion docked.

The two latest outgoing ships were carrying almost 59,000 tonnes of corn and soybeans and were bound for Italy and southeastern Turkey following inspections. The four that left on Sunday bore almost 170,000 tonnes of corn and other food.

The July 22 grain export pact brokered by Turkey and the United Nations represents a rare diplomatic triumph as fighting churns on in Ukraine and aims to help ease soaring global food prices arising from the war.

Before Moscow's invasion, Russia and Ukraine together accounted for nearly a third of global wheat exports. The disruption since then has raised the spectre of famine in parts of the world.

GRINDING BATTLE FOR DONBAS

Russia says it is waging a "special military operation" in Ukraine to rid it of nationalists and protect Russian-speaking communities. Ukraine and the West describe Russia's actions as an unprovoked imperial-style war to reassert control over a pro-Western neighbour lost when the Soviet Union broke up in 1991.

The conflict has displaced millions, killed thousands of civilians and left cities, towns and villages in ruins.

It has evolved into a war of attrition concentrated in the east and southeast of Ukraine.

Russian President Vladimir Putin's forces are trying to gain full control of Ukraine's eastern Donbas region where pro-Moscow separatists seized territory after the Kremlin annexed Crimea to the south in 2014.

"Ukrainian soldiers are firmly holding the defence, inflicting losses on the enemy and are ready for any changes in the operational situation," Ukraine's general staff said in an operational update on Monday.

Russian forces stepped up attacks north and northwest of Russian-held Donetsk city in the Donbas on Sunday, Ukraine's military said. It said the Russians attacked Ukrainian positions near the heavily fortified settlements of Piski and Avdiivka, as well as shelling other locations in Donetsk province.

In addition to tightening its grip over the Donbas, Russia is entrenching its position in southern Ukraine, where it has gathered troops in a bid to prevent a potential counter-offensive near Kherson, Kyiv has said.

Russia's Interfax news agency quoted a Russian-appointed official in the southeastern city of Kherson as saying on Monday Ukrainian forces had again shelled the Antonivskyi bridge there, damaging construction equipment and delaying its reopening.

The bridge is one of only two crossing points for Russian forces to territory they have occupied on the western bank of the major Dnipro river in the south.

It has been a key Ukrainian target in recent weeks, with Kyiv using high-precision U.S.-supplied rockets to try to destroy it in possible preparation for a counter-attack.


READ MORE: Latest development on Ukraine-Russia crisis