The oldest son of former Alaska governor Sarah Palin was arrested in a domestic violence case in which his girlfriend was afraid he would shoot himself with an AR-15 assault rifle.

Track Palin, 26, was charged with assault, interfering with the report of a domestic violence crime and possessing a weapon while intoxicated following the incident on Monday night at the Wasilla, Alaska, home of his parents, where he lives, according to an affidavit by police.

The girlfriend told authorities she was punched in the face by Palin, who is the oldest child of Sarah Palin, the 2008 Republican vice presidential nominee and a conservative leader.

The charges were filed on Tuesday, the same day Sarah Palin appeared in Iowa to endorse Republican presidential frontrunner Donald Trump.

Court documents say the victim, Track Palin's girlfriend of one year, had bruising and swelling around her left eye, and she said her right knee hurt after he kicked her.

Palin family lawyer John Tiemessen declined to comment on the matter other than to say that respect for the family's privacy is appreciated "as Track receives the help that he and many of our returning veterans need".

Track Palin spent a year deployed in Iraq with the Army, after he enlisted on the sixth anniversary of the September 11, 2001, terrorist attacks.

According to the three-page affidavit, both Palin and his girlfriend called the emergency dispatcher that night.

Police officer Andrew Kappler wrote that he arrived at the Wasilla home and found Track Palin walking outside and talking on a phone. The officer said Palin had an injury to his right eye and surrounding area, smelled strongly of alcohol and acted with escalating hostility, prompting Mr Kappler to put him in handcuffs.

The affidavit says other officers found the girlfriend hiding under a bed inside the home and crying.

The affidavit says the woman said Palin struck her with his fist on the left side of her head near her eye. She said he then kicked her in the knee.

Palin held the rifle, with the barrel just away from his face pointed to the side, the affidavit states, and the woman told police Palin was yelling: "Do you think I won't do it?"

The girlfriend "was concerned that he would shoot himself and ran outside and around the house," the affidavit says."

It is not the first encounter with the law for Palin or other members of his family.

In September 2014, he and other Palins were involved in a brawl that broke out at a party in Anchorage. No arrests were made, and no-one wanted to press charges. But according to a police report, Palin had blood around his mouth and his hands. He was belligerent until his mother told him to talk to a police officer.