Rafael Grossi, the head of the U.N. nuclear inspector, said on Saturday that he will go to the Russian-controlled Zaporizhzhia nuclear power station in Ukraine the next week to assess the critical circumstances there.

Grossi is pushing for the construction of a security perimeter around the six-reactor facility, which is the largest nuclear power station in Europe and has endured repeated shelling in recent months.

It will be his second visit. Last September he went there and established a permanent presence of IAEA experts.

Russian troops occupied the facility early in their invasion of Ukraine and it remains near the front line. Both sides blame each other for the shelling.

“The situation at the Zaporizhzhia nuclear power plant is still precarious,” Grossi said in the statement, saying he wanted “to assess first-hand the serious nuclear safety and security situation at the facility”.

Earlier this month he appealed for the protection zone around the plant to be set up, saying he was “astonished by the complacency” around the issue.

The plant accounted for around 20% of Ukraine’s national power generation before the invasion, but has not produced any electricity since September when the last of its six reactors was taken offline.