Two police officers walk near the building of the confectionery factory "Menshevik" in Moscow, Russia, where a gunman earlier opened fire, on December 27, 2017. (Xinhua/Wu Zhuang)

MOSCOW, May 5 (Xinhua) -- Russian security officers killed an unidentified man after he fired at them in Nizhny Novgorod city, about 400 km east of Moscow, the Federal Security Service (FSB) said Saturday.

The man attacked law enforcement officers during a document-checking procedure and hid in an apartment building, according to a FSB statement.

He refused to lay down his arms and opened fire and was subsequently neutralized, the statement said.

Three security officers were reportedly injured.