A State Police trooper allegedly choked his girlfriend in their Boxborough apartment Saturday morning, leading to his arrest by fellow troopers that night, authorities said.

The 45-year-old trooper has been charged with assault on a family or household member and strangulation. He was immediately relieved of duty pending an internal review, State Police spokesman Dave Procopio said in a statement.

Procopio said investigators believe the trooper restrained his girlfriend, “choked her with his hands on her throat, and at one point put her in a choke hold before she was able to break free.’’

“After the assault ended, the victim waited until the defendant apparently fell asleep and then fled the apartment,’’ Procopio added.

The victim reported the assault to State Police later in the day, and the trooper was arrested by his colleagues at the apartment that night.

“The State Police, while cognizant that the charges are allegations until proven in a court of law, nonetheless condemn the facts as alleged and have no tolerance for domestic violence,’’ said Procopio.

State Police are not releasing the name of the trooper, citing a state law that prohibits police from identifying suspects charged with domestic violence. The Middlesex district attorney’s office, which will prosecute the case, declined to provide any details in advance of an arraignment scheduled for Monday morning in Ayer District Court.

The trooper is assigned to the Concord barracks and joined the State Police about 14 years ago, according to Procopio.

“His department weapons, equipment, and identification were confiscated from him, and his license to carry a firearm was immediately suspended,’’ said Procopio.

He said the department will hold a hearing early in the week to further discuss the trooper’s status. The State Police Internal Affairs Section is also investigating and will monitor the criminal case, Procopio said.

The trooper was booked at the State Police barracks in Danvers, with bail set at $500,000 cash. Procopio said that the victim has been advised of her right to seek a restraining order.

Nicole Fleming can be reached at nicole.fleming@globe.com.