Police arrested a woman suspected of drug-dealing with her 2-year-old child in the car, San Francisco police said Friday.

The 21-year-old mother has been under investigation for a month by drug cops for suspected dealing offenses in the Tenderloin neighborhood, police said. The child was placed in the custody of a relative.

The suspect was arrested at 2:40 p.m. Tuesday after officers searched her car on Russ Street between Howard and Folsom streets in the SoMa neighborhood. Police seized narcotics from her at the time of her arrest.

Narcotics Unit officers, Tenderloin officers and the Drug Enforcement Agency then searched two Oakland residences in the Eastmont and Brookfield Village neighborhoods believed to be linked to the suspect. Officials say they found a loaded firearm, along with suspected fentanyl, methamphetamine, base rock cocaine, heroin, Oxycodone and Xanax. Police say roughly 3.5 pounds of drugs were seized due to the investigation and searches.

The suspect was booked on suspicion of reckless child endangerment and several drug charges, including possession of fentanyl, methamphetamine, heroin and cocaine. She is scheduled to appear in court on Friday.

A multi-agency crackdown on drug dealing began in San Francisco in the spring, with a command center opening in the Market Street area in June.