BORODYANKA/LVIV: The Zaporizhzhia nuclear power plant in Ukraine, the largest of its kind in Europe, was on fire early on Friday after an attack by Russian troops, the mayor of the nearby town of Energodar said.

There has been fierce fighting between local forces and Russian troops, Dmytro Orlov said in an online post, adding that there had been casualties without giving details.

Earlier, Ukrainian authorities reported Russian troops were stepping up efforts to seize the plant and had entered the town with tanks.

"As a result of continuous enemy shelling of buildings and units of the largest nuclear power plant in Europe, the Zaporizhzhia nuclear power plant is on fire," Orlov said on his Telegram channel, citing what he called a threat to world security. He did not give details.

Radiation levels within control

The International Atomic Energy Agency said on Twitter that it's been informed by Ukraine's nuclear regulator that there has been no change reported in radiation levels at a nuclear power station shelled by Russian troops. 

The agency said its Director General Mariano Grossi was in touch with Ukraine's Prime Minister Denys Schmygal and the Ukrainian regulator and operator about the situation at the Zaporizhzhia plant. 

Grossi appeals for halt of use of force and warns of severe danger if reactors hit, the IAEA said in another tweet.

An official in Ukrainian President Volodymyr Zelenskyy's office, not authorized to speak publicly and speaking on condition of anonymity, said the reactors have not yet been damaged and radiation levels are normal. 

However, a government official told The Associated Press elevated levels of radiation are being detected near the site of the Zaporizhzhia nuclear plant, which provides about 25% of the country's power generation. The official spoke on condition of anonymity because the information has not yet been publicly released.

Plant spokesman Andriy Tuz told Ukrainian television that it is urgent to stop the fighting to put out the flames.

Enerhodar is a city on the Dnieper River that accounts for one-quarter of the country's power generation.

The fighting at Enerhodar came as another round of talks between the two sides yielded a tentative agreement to set up safe corridors inside Ukraine to evacuate citizens and deliver humanitarian aid.

U.S. Energy Secretary Jennifer Granholm said the reactors at Ukraine's Zaporizhzhia nuclear power station "are protected by robust containment structures and reactors are being safely shut down".

Granholm said on Twitter she had just spoken with Ukraine's energy minister about the situation at the plant, where a fire broke out during fighting between Russian and Ukrainian forces.

"We have seen no elevated radiation readings near the facility," Granholm said.

Biden seeks update from Zelenskyy

US President Joe Biden spoke with his Ukrainian counterpart Volodymyr Zelenskyy to receive an update on the fire at the Zaporizhzhia Nuclear Power Plant and urged Russia to cease its military activities in the affected area and allow access to emergency responders, the White House has said.

Biden also spoke with the Under Secretary for Nuclear Security of the US Department of Energy and Administrator of the National Nuclear Security Administration (NNSA) to receive an update on the situation at the plant.

Heavy fighting continues

Thousands are thought to have died or been wounded as the biggest attack on a European state since World War Two unfolds, creating 1 million refugees, hits to Russia's economy, and fears of wider conflict in the West unthought-of for decades.

The incursion is entering its ninth day.  

The Russians announced the capture of the southern city of Kherson, a vital Black Sea port of 280,000, and local Ukrainian officials confirmed the takeover of the government headquarters there, making it the first major city to fall since the invasion began a week ago.

Heavy fighting continued on the outskirts of another strategic port, Mariupol, on the Azov Sea.

The battles have knocked out the city's electricity, heat and water systems, as well as most phone service, officials said. Food deliveries to the city were also cut

Severing Ukraine's access to the Black and Azov seas would deal a crippling blow to its economy and allow Russia to build a land corridor to Crimea, seized by Moscow in 2014.

Overall, the outnumbered, outgunned Ukrainians have put up stiff resistance, staving off the swift victory that Russia appeared to have expected. But a senior US defense official, speaking on condition of anonymity, said Russia's seizure of Crimea gave it a logistical advantage in that part of the country, with shorter supply lines that smoothed the offensive there.

Ukrainian leaders called on the people to defend their homeland by cutting down trees, erecting barricades in the cities and attacking enemy columns from the rear.

Russia has fired more than 480 missiles in the invasion, according to the US Ukrainian officials boasted that their missile-defense systems shot down many of them.

At least 227 civilians have been killed and 525 wounded, according to the office of the UN High Commissioner for Human Rights, though it acknowledged that is a vast undercount, and Ukraine said more than 2,000 civilians have died. The figures could not be independently verified.

Russia reported its military casualties Wednesday for the first time in the war, saying nearly 500 of its troops have been killed and almost 1,600 wounded.

Ukraine insisted Russia's losses are many times higher but did not disclose its own military casualties.

(With inputs from Reuters, AP via PTI.)