BORODYANKA/LVIV: The largest nuclear power plant in Europe is on fire following a Russian attack, Ukraine's foreign minister said on Friday, as he called for a security zone and firefighters to be allowed to tackle the incident.

A generating unit at the plant has been hit during an attack by Russian troops and part of the station is on fire, RIA news agency cited the Ukrainian atomic energy ministry as saying on Friday.

A plant spokesperson told RIA that background levels of radiation had not changed.

"Russian army is firing from all sides upon Zaporizhzhia NPP, the largest nuclear power plant in Europe," Foreign Minister Dmytro Kuleba wrote on Twitter.

"Fire has already broke out ... Russians must IMMEDIATELY cease the fire, allow firefighters, establish a security zone!"

There has been fierce fighting in the area about 550 kilometers (342 miles) southeast of Kyiv, the mayor of the nearby town of Energodar said in an online post. He said there had been casualties, without giving details.

Russia has already captured the defunct Chernobyl plant, some 100 km north of Ukraine's capital, Kyiv.

The International Atomic Energy Agency said in a tweet that it was "aware of reports of shelling" at the power plant and was in contact with Ukrainian authorities about situation.

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.

Reuters could not immediately verify the information, including the potential seriousness of any fire.

As the biggest attack on a European state since World War Two enters its ninth day, thousands are thought to have died or been wounded, 1 million refugees have fled Ukraine and Russia's economy has been rocked by international sanctions.

On Thursday, the United States and Britain announced sanctions on more Russian oligarchs, following on from EU measures, as they ratcheted up the pressure on the Kremlin.

Sanctions have "had a profound impact already," said U.S. President Joe Biden.

Russia calls its actions in Ukraine a "special operation" that is not designed to occupy territory but to destroy its neighbour's military capabilities and capture what it regards as dangerous nationalists. It denies targeting civilians.

READ MORE: Latest developments on Ukraine-Russia crisis