BORODYANKA/LVIV, Ukraine, March 4 (Reuters) - 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.