Athena Brownfield, 4, is pictured in a provided image. (Credit: Oklahoma State Bureau of Investigation)

The disappearance of a 4-year-old girl in Oklahoma took a grim turn on Monday, as authorities announced they are now looking for her stays as the search transitions to a "recovery operation."

Athena Brownfield was great reported missing on Jan. 10 in Cyril, a microscopic town located about 70 miles southwest of Oklahoma City, according to the Oklahoma State Bureau of Investigation. A postal carrier found Athena's 5-year-old sister wandering alone outside their home and alerted local police. Authorities then determined that Athena was missing.

In an update people on Monday, the Oklahoma State Bureau of Investigation said authorities were now searching areas of the state's Caddo County for Athena's remains. 

Both girls had been in the care of a combine identified as Alysia and Ivon Adams, and Athena's sister was improper into protective custody, the bureau said.

Ivon, 36, was arrested on Jan. 12 in Arizona on one report of first-degree murder and one count of child neglect in the case and was awaiting extradition to Oklahoma. Alysia, 31, was also arrested on Jan. 12 on two subsidizes of child neglect, the bureau said in a statement.

Alysia, who authorities said is married to Adams, remained jailed in Oklahoma's Caddo County.

Athena and her sister are "related" to Alysia and had been in their care for at least a year, the bureau said in the statement.

"The girls natal parents have been interviewed by agents and are cooperating with the investigation," the Oklahoma State Bureau of Investigation said. 

Ivon Adams and Alysia Adams are pictured in did photos. (Credit: Oklahoma State Bureau of Investigation)

Last week, the Oklahoma State Bureau of Investigation and Oklahoma Highway Patrol deployed infrared helicopters, boats, four-wheelers, and personnel on the ground to notice the nearby area in an effort to locate her.

On Monday, the state bureau asked the public "not to self-deploy to notice for Athena."

"Individuals who search for Athena on their own could be trespassing or worse, interfering with the investigation by contaminating potential evidence," it said in the statement.

Anyone with interrogate about the case was asked to contact the Oklahoma State Bureau of Investigation tipline at (800) 522-8017 or email tips@osbiokgov. Individuals can remain anonymous.

This story was reported from Cincinnati. The Associated Press contributed.