Five employees of Russia’s atomic agency have been killed in a blast at a military test site in northern Russia, the state-run Rosatom said Saturday.

The five were killed “while testing a liquid jet propulsion system,” Rosatom, which oversees all Russian nuclear projects, said in a statement on its website, as reported by CNN. It added three more people were injured and “have burns of varying severity.”

The incident happened Thursday near Severodvinsk, a town in the Arkhangelsk region which is home to a naval base and a shipyard.
The Russian Defense Ministry said at the time that two people died while testing the liquid jet propulsion system and that no dangerous substances were released into the atmosphere. “The tragedy occurred during works related to the engineering and technical support of isotopic sources in a liquid propulsion system,” the ministry said in a statement.

However, local authorities in Severodvinsk released a statement Thursday that said there was a radiation spike following the blast. That statement has since been deleted from the official website.

A spokesperson for the Severodvinsk administration told RBC, a Russian daily business newspaper, that the statement had been removed from the website “as the situation is being handled by the Ministry of Defense.”

The local authorities said sensors in Severodvinsk “recorded a short-term increase in the radiation background” at 11:50 a.m. local time (4:50 a.m. ET) on Thursday. The statement went on to say the radiation level decreased between 11:50 a.m. and 12:30 p.m. local time. It added that by 2 p.m. the radiation levels in Severodvinsk had returned to normal.

The blast near Severodvinsk is one of the three incidents which took place in Russia this week as two explosions rocked an ammunition storage facility in the Krasnoyarsk region injuring dozens.