Ukraine announced on Monday the start of a long-awaited counteroffensive to reclaim territory in the south seized by the Russian forces since invasion six months ago, a move reflecting Kyiv's growing confidence as Western military aid flows in.

"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. She confirmed the news minutes later at a briefing.

Ukraine has been talking up a planned counteroffensive 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.

Meanwhile, the governor of Ukraine's Russian-annexed Crimean Peninsula, Sergei Aksyonov, dismissed the announcement of a counteroffensive on Telegram as "another fake of Ukrainian propaganda." Crimea is adjacent to the Kherson region.

The news came as a team from the U.N. nuclear watchdog headed to Ukraine to inspect the Zaporizhzhia nuclear plant – captured by Russian forces in March but still run by Ukrainian staff – that has become a hot spot in the war.

Moscow and Kyiv have traded accusations of shelling in the vicinity of the nuclear plant, Europe's largest and close to frontlines in the war, amid fears of a radiation disaster in a country still haunted by the 1986 Chornobyl disaster.