Lina Sadar Khil went missing from a San Antonio playground in her family's apartment complex on December 20, 2021.
CNN  — 

The FBI’s underwater search and evidence response team has joined the search for 3-year-old Lina Sadar Khil, who went missing last month from a San Antonio playground in her family’s apartment complex, city police said.

Lina was last seen December 20 after her mother left her unattended for a period of time at the playground. When the mother returned, her daughter was gone, San Antonio Police Chief William McManus said.

The FBI’s dive team is using special equipment and technology, according to police.

“They flew in from Washington DC last night and have been here all day,” McManus said during a news conference Tuesday. “I wish I could be more uplifting. I know this looks like we are onto something, but all we’re doing here is following up on leads. We don’t want to leave anything to chance. Everything that we get that has any kind of potential at all, we’re following it up.”

McManus declined to describe his confidence in the lead the police are pursuing.

“I mean, so far, none of the leads have led us to Lina, so I don’t know if you can compare them that way. It’s a lead, and we’re following up it,” McManus said.

The child’s family is among the Afghanistan refugees in San Antonio, and it is unclear when the family arrived in the United States, according to CNN affiliate KSAT.

The Islamic Center of San Antonio has offered a $100,000 reward for anybody who could provide information that would help find Lina.

She was last seen wearing a red dress, black jacket and black shoes, police said. She weighs 55 pounds, has brown eyes and straight brown hair with a light skin complexion.

McManus encouraged anyone who has information to contact his department’s Missing Person’s Unit at 210-207-7660.

CNN’s Tina Burnside contributed to this report.