SAN FRANCISCO — A man was arrested and placed under psychiatric evaluation Monday night on suspicion of using his cellphone to make bomb threats while riding a BART train through San Francisco, authorities said Tuesday. His name has not been released.

After the man was detained at the Daly City station, both the train he had been on and the San Francisco International Airport station where it had later stopped were evacuated for a time after an unattended backpack was found on the train, authorities said.

The unfolding incident began about 8:50 p.m. Monday when the Alameda County Sheriff’s Office reported to BART authorities that a man was making bomb threats via his cellphone on social media.

BART police said there were no direct threats made toward the BART system but it was not disclosed who or what were the target of the threats.

Authorities were able to trace the cellphone to the area of the BART Embarcadero Station but the man was not found there.

He was later found on a train at the Daly City Station and taken into custody, authorities said.

A patron later contacted police saying there was an unattended backpack on the same train. Authorities apparently believed the backpack belonged to the man detained in Daly City.

The train was held at the San Francisco International Airport Station and it was evacuated along with the station while authorities deemed the backpack safe.

Authorities said the man was placed on a psychiatric hold and also a criminal hold on suspicion of terrorist threats and false bomb threats.

It was not immediately known what the impact of the investigation and closing the airport station had on the BART system.

Check back for updates.