Authorities are investigating the disappearance of two women in western Oklahoma, who were last seen together in a vehicle later found abandoned in a rural area near the highway. Law enforcement said 27-year-old Veronica Butler and 39-year-old Jilian Kelley went missing under "suspicious" circumstances.

The Oklahoma State Bureau of Investigation on Sunday announced its involvement in the probe at the request of the Texas County Sheriff's Department, whose jurisdiction includes the isolated part of the Oklahoma panhandle where the women's car was discovered. 

Oklahoma Highway Patrol issued an Endangered Missing Advisory for Butler and Kelley, on behalf of the sheriff's department, on Saturday. That alert deemed both women "at-risk," although few details have been shared publicly about the events leading up to their disappearance. 

Butler and Kelley were "traveling to pick up children" before they vanished, according to the missing persons alert, which noted that neither "made it to the pick up location." Their car was found abandoned along the side of the road near Oklahoma State Highway 95, which is just south of Elkhart, Kansas, right over the border with Oklahoma.

Highway Patrol released images of Butler and Kelley along with written descriptions of the women. Butler is 5 feet 4 inches tall with red hair and green eyes, and she wore a blue short-sleeved shirt, denim shorts and shoes by the brand Hey Dude when she disappeared, according to the alert. She also has several tattoos, includes a Chinese symbol on her left forearm and a sunflower on her left shoulder.

Kelley has brown hair and blue eyes, and she was wearing a long-sleeved shirt, white-washed blue jeans and tan or beige-colored shoes when she went missing. Kelley has a butterfly tattoo on her left forearm.

State investigators said they are working with local law enforcement agencies to find Butler and Kelley. They have asked anyone with information about the women's whereabouts to contact the bureau.

CBS News contacted the Oklahoma Bureau of Investigation for more information about the women's disappearance and the missing persons case but did not receive an immediate reply.