A Medford mom accused of killing her 2-year-old twin daughters was arraigned on new, upgraded charges Wednesday.

Tenia Campbell, 24, was previously charged with second-degree murder, but now faces two counts of first-degree murder. Campbell pleaded not guilty in court.

Prosecutors say she killed her twins, Jasmine and Jaida, back in June. They say Campbell allegedly called her mother saying she killed the girls with her bare hands as she drove from Medford to Montauk.

A three-way phone call ensued that lasted 12 minutes between police, Campbell, and Campbell's mother. During that time, police say the suspect refused to tell them where she was and claimed the girls were already dead.

An Amber Alert was issued, and police say they used cellphone GPS to find Campbell near a nature center in Montauk.

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Officials say that Campbell had parked her car at the entrance to the park, walked to Montauk Highway, and started screaming at responding officers to shoot her.

The girls were found in their car seats around 4 p.m. Police say officers at the scene tried to perform lifesaving first aid on the girls. They were also rushed to a hospital but could not be saved.

Prosecutors say the girls were suffocated. Campbell's attorney says she suffers from a history of mental illness, and has put in an application asking for a doctor to evaluate her mental state.

Campbell remains on suicide watch. She is being held without bail. If convicted, she faces life in prison without the possibility of parole.