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Aug. 16 update: Christopher Watts, the husband of a pregnant Frederick woman who has been missing along with his two young daughters since Monday has been arrested. Read more here.

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FREDERICK, Colo. — A pregnant woman and her two children have been reported missing, the Frederick Police Department said Tuesday morning.

Shanann Watts, 34, and her 3- and 4-year-old daughters were reported missing on Monday. Watts is 15 weeks pregnant, police said.

Police released very little information, only saying no vehicle has been associated with the disappearance.

A majority of the police department is working to find Watts and her daughters, Bellaa and Celeste “Cece.”

Watts is described as being 5-foot-5 and 148 pounds with black hair and hazel eyes.

On Wednesday morning, the FBI and the Colorado Bureau of Investigation were brought in to assist with the investigation.

Police have not said if they suspect foul play is associated with the disappearances and were not specific where Watts and her daughters were last seen.

A close friend said she dropped off Watts at home about 2 a.m. Monday when they got home from a work trip. She saw her go inside.

She said the two friends were supposed to meet later in the day, but Watts didn’t answer her phone.

“I called her and texted her several times,” Watts’ friend said. “I knew she had a doctor’s appointment that morning because she’s pregnant. She didn’t show up for it … and I was even more concerned.”

Watts’ friend said she called police on Monday and walked through the house with officers as they did a welfare check.

She said Watts’ purse, keys and phone were found inside.

“I don’t know where she’s at. This is completely unlike her,” the friend said.

Police confirm the behavior is out of character and that’s why they’re concerned. They searched the neighborhood with K-9s and officers most of the day.

“My heart is racing a mile a minute,” husband Chris Watts said.

“It’s not something I could ever, ever fathom would happen in my lifetime, and I have no inclination of where she is. She said she was going to a friend’s house with the kids and that’s the last thing I heard, and that was it. It was very vague.”

Chris Watts said he’s hopeful his two girls and his wife are OK.

Frederick is in Weld County, about 15 miles southeast of Longmont.

Anyone with information is asked to call police at 303-652-4222 or email.

Shanann Watts and her two children. (Photos: Frederick Police Department)