A military rocket launcher was discovered on the side of the I-15 Freeway in Riverside County, California, Thursday afternoon, officials said.

It was unclear who the weapon belonged to, said a Riverside County Sheriff's Department spokesman. Rocket launchers are illegal to own, though some are occasionally found in California.

Workers clearing brush from the side of the highway in Murrieta found the rocket launcher, according to Patch, which first reported the discovery.

The AT-4 tube had no munitions inside, officials said. Its manufacturer's web page described it as "one of the most successful anti-armour weapons ever developed," effective against armorded vehicles and aircraft.

A rocket launcher was returned to law enforcement at a 2013 gun buyback in Solano County, and officers in 2012 found a rocket launcher while executing a search warrant in Paramount.