MOSCOW (Reuters) - Three people were killed and four injured in a blast on Friday at an explosives plant in the Russian city of Dzerzhinsk, 400 km east of Moscow, local officials said.

An investigation to establish the cause of the blast was underway at the plant, which belongs to state-run manufacturer Sverdlov, the local branch of the Investigative Committee said in a statement on its website.

Mikhail Lebedev, Sverdlov’s acting director was quoted by RIA news agency as saying the blast was an accident which occurred while workers were destroying old anti-tank mines for the Ministry of Defence.

Five people were still missing, Lebedev said.

In a separate incident on Friday, two workers were killed in a blast in the region of Samara at the Kuznetsov factory which manufactures rocket and aircraft engines for state arms conglomerate Rostec.

That accident happened when an oxygen tank was being cleaned, investigators said.