"Today we started offensive actions in various directions, including in the Kherson region," Ukrainian public broadcaster Suspilne cited southern command spokesperson Natalia Humeniuk as saying on Monday.

She confirmed the news minutes later at a briefing.

Ukraine has been talking up a planned counter-offensive in its Russian-occupied southern regions for two months.

Humeniuk said that Ukraine's recent strikes on Russia's southern logistical routes had "unquestionably weakened the enemy," adding that more than 10 Russian ammunition dumps had been hit over the last week.

However, she declined to be drawn into giving more details about the new offensive.

"Any military operation needs silence," she said, adding that Russia's forces in the south are "rather powerful" and have been built up over a long time.

News of the offensive comes as a team from the UN nuclear watchdog is heading to Ukraine's Zaporizhzhia nuclear plant, the agency's chief says, as Russia and Ukraine trade accusations of shelling in its vicinity, fuelling fears of a radiation disaster.

Captured by Russian troops in March but run by Ukrainian staff, Zaporizhzhia has been a hotspot in a conflict that has settled into a war of attrition fought mainly in Ukraine's east and south six months after Russia launched its invasion.

"We must protect the safety and security of Ukraine's and Europe's biggest nuclear facility," Rafael Grossi, director-general of the International Atomic Energy Agency (IAEA), said in a post on Twitter on Monday.

A team of IAEA inspectors he is leading will reach the plant on the Dnipro river near front lines in southern Ukraine this week, Grossi said, without specifying the day of their arrival.

The IAEA tweeted separately that the mission would assess physical damage, evaluate the conditions in which staff are working at the plant and "determine functionality of safety & security systems". It would also "perform urgent safeguards activities", a reference to keeping track of nuclear material.

The Kremlin said on Monday the IAEA mission was "necessary" and urged the international community to pressure Ukraine to reduce military tensions at the plant.

With fears mounting of a nuclear accident in a country still haunted by the 1986 Chornobyl disaster, Zaporizhzhia authorities are handing out iodine tablets and teaching residents how to use them in case of a radiation leak.

Russian forces fired at Enerhodar, the Dnipro riverside town where the plant is located, the chief of staff of Ukrainian President Volodymyr Zelenskiy, said late on Sunday on his Telegram channel alongside a video of firefighters dousing burning cars.

"They provoke and try to blackmail the world," Andriy Yermak said.

Russia's defence ministry said its forces had shot down a Ukrainian drone that was trying to attack the nuclear power station, Russian news agencies reported. It said there was no serious damage and radiation levels were normal.

In the Donetsk region of eastern Ukraine, Russian forces shelled military and civilian infrastructure near Bakhmut, Shumy, Yakovlivka, Zaytsevo, and Kodema, Ukraine's military said early on Monday.

Russian strikes killed eight civilians in Donetsk province on Sunday, its governor Pavlo Kyrylenko said.

Sweden, which along with Finland is pressing to join NATO in response to Russia's invasion, announced nearly $US50 million worth of additional military aid to Ukraine on Monday during a visit to Stockholm by Ukrainian Foreign Minister Dmytro Kuleba.

Germany will also send more weapons to Ukraine in the coming weeks and help build up the country's artillery and air defence capacities, Chancellor Olaf Scholz told a conference in Prague, where he also reaffirmed Berlin's support for Ukraine and several other ex-Soviet republics to join the European Union.

Australian Associated Press