OKLAHOMA CITY (Reuters) - The U.S. Marshals Service has joined the search for an Oklahoma man suspected of wounding two police officers in a shootout, stealing a police truck, killing his aunt and uncle and making social media posts of his escape, authorities said on Tuesday.

The Marshals Service said it was taking part in the search for 38-year-old Michael Vance, wanted in Sunday's slayings in the town of Luther about 30 miles northeast of Oklahoma City, but did not specify its role.

Vance is suspected of killing Ronald Wilkson, 55, and his wife Valerie Wilkson, 54, and trying to decapitate them at their home, the Oklahoma County Sheriff's Office said.

Vance is thought to have killed his aunt and uncle about three hours after the shootout with police, the sheriff's office said. The officers were responding to a call of shots being fired. Both suffered wounds that were not life threatening.

Vance, who appeared to have been shot in the gunfight with the officers, also has an infectious disease that he may be trying to spread, local law enforcement said. In July, he was charged with child sexual abuse, the Oklahoma County Sheriff's Office said.

In a video posted on Facebook Live while fleeing, Vance can he heard saying he is about to steal another car and that the chase has been "intense."

"This ain't a joke. This ain't a prank," Vance said, adding he was set up.

Vance also stated in the video that he was shot. The Oklahoma County Sheriff's Office said there appears to be a large amount of blood on his shirt and a rifle or shotgun next to him in the vehicle.

Vance is suspected of shooting at least two people in attempts to steal vehicles. Both people survived, local law enforcement said.

(Reporting by Jon Herskovitz, Addiitional reporting by Heide Brandes in Oklahoma City; Editing by Will Dunham)