Father Andrei Nikolayev died early Saturday along with his children when their wooden house in the central Tver region, about 160 kilometers (100 miles) northwest of Moscow, caught fire, regional Prosecutor Sergei Yagodkin said.
Investigators were working to determine whether a fifth body discovered in the house was that of Nikolayev's wife, said Galina Malyuta, a prosecutors' spokeswoman. Authorities had believed the wife was in a hospital when the fire broke out.
Malyuta said a murder investigation had been opened and investigators considered arson to be the likely cause.
Pravoslaviye i Mir, an online Orthodox news site, said that the priest's home was doused with gasoline and set on fire. It claimed that local residents, many of them heavy drinkers, had repeatedly tried to rob the local church and threatened the priest, reports AP.
Regional Governor Dmitry Zelenin said he would personally oversee the probe, the RIA Novosti news agency reported.
"It's known that the priest had a conflict with certain people who tried to rob the church and repeatedly threatened him," he was quoted as saying.