Russian forces controlling Ukraine's Zaporizhzhia nuclear power plant have killed two staff at the facility and detained and abused dozens of others, the head of Ukraine's nuclear energy agency told AFP on Friday.

The Zaporizhzhia plant -- the largest in Europe -- was captured by Russian troops in March. An uptick in fighting around it in recent weeks has raised fears of a nuclear disaster with both Moscow and Kyiv blaming the other for the escalation.

"A regime of harassment of personnel was gradually established," following the Russian takeover, Petro Kotin said.

"Two people were beaten to death. We do not know where about ten people are now, they were taken (by the Russians) and after that we have no information about their whereabouts," Kotin said, adding about 200 people had been detained.

He described the current situation at the plant as "very difficult," citing "torture" of staff and "beatings of personnel.

"The Russians look for pro-Ukrainian people and persecute them. People are psychologically broken," he said in an interview with AFP reporters in his office in Kyiv.

Frequent shelling of the plant -- including the town of Energodar where the facility is located -- means staff have been trying to secure safe passage for family members to leave the area, Kotin said.

"Two people on the territory of the plant were wounded during shelling -- a woman and a man -- on separate occasions," Kotin, clad in a military-style jacket, said.

"But people understand that the nuclear safety of the plant depends on them, so the employees return to Energodar and continue working at the facility," he added.

- Demilitarisation zone needed -
 

The UN International Atomic Energy Agency (IAEA) dispatched a 14-strong mission last week to the plant and released a report following the inspection.

Kotin said it described difficult psychological working conditions at the plant that ultimately amounted to "a violation of nuclear radiation safety.

"This situation must be corrected as soon as possible," he told AFP.

The IAEA in its report called for "the immediate establishment of a nuclear safety and security protection zone" around the plant as it faces an "untenable" situation.

But Kotin said there was room for interpretation there.

"If this is the demilitarisation of the nuclear plant, we fully support it. If it is ... the creation of some security zones with joint control along with the Russians, then this is of course an unacceptable decision for us," Kotin said.

"We will insist on creating a demilitarised zone around the plant, including with the participation of peacekeeping groups," he added.

Kotin also said Ukraine insists that Russia remove military hardware from the plant and that staff from Russian nuclear agency Rosatom also leave the area.

"For this, international partners need to put a lot of pressure on Russia to meet conditions that the Ukrainian authorities and the IAEA have made."

Kotin added all power lines connected to the plant have been severed as a result of shelling and the only reactor still on "is operating at a very low power level".

If these power lines are not restored, Kotin said, the station will go into blackout mode and will be able to rely only on diesel engines "to cool the nuclear material".

The head of the IAEA meanwhile on Friday echoed the point, saying nearby shelling had caused a blackout in Energodar and compromised safe operation of the plant.

Director General Rafael Grossi in a statement on social media described the recent shelling as a "dramatic development".

"This is completely unacceptable. It cannot stand," he added.

"It is necessary to renew the communication line with the Ukrainian power system as soon as possible and supply it with power from external sources of energy supply," Kotin stressed.