MOSCOW- A Russian court has placed the head of a processing plant owned by metals producer Norilsk Nickel in Siberia under house arrest as officials investigate an accident at the plant, Interfax news agency reported on Thursday.

A section of the plant collapsed on Feb. 20 killing three workers during renovation works. A regional investigative committee had opened a criminal investigation into the accident. 

The plant's head, Alexander Tsymbal was placed under house arrest until April 20 as he is suspected of violating safety rules during the renovation works, Interfax quoted the Krasnoyarsk regional court as saying.

The plant's chief engineer and head of technical inspection are also suspected of the same violations. They were detained until April 19 by another court's decision earlier on Thursday, the court said in a statement on its website.

Tsymbal had been suspended from his post, Nornickel said on Feb. 20, when the accident happened, adding that it would tighten requirements for industrial safety.

Nornickel's shares have been falling this week as the accident was followed by partial suspension of operations at its two major mines in Siberia due to an inflow of water underground. 

The miner's shares were last down 4% in trading in Moscow on Thursday, underperforming the benchmark index , which is up 0.7%.

(Reporting by Polina Devitt; editing by Emelia Sithole-Matarise) ((Polina.Devitt@thomsonreuters.com))