An unidentified attacker murdered a police officer using a knife early on Sunday in southwestern Moscow, local police said.

"The policeman was seriously wounded in south-west Moscow and later died from sustained injuries," a police spokesman said without revealing details of the incident.

Another police source told RIA Novosti that the officer was off duty and got in a quarrel with a car driver.

A criminal investigation into the murder has been launched.

According to police, the attacker could be a resident of one of Russia's North Caucasus republics.

On Friday night, one police officer was killed and another wounded in a shootout with members of a criminal group in a northwestern suburb of Moscow.

The suspected leader of the group, a Tajik national, was arrested in Moscow on Saturday.

MOSCOW, December 27 (RIA Novosti)