PORTLAND — The father of Ayla Reynolds, the toddler whose disappearance generated national attention, pleaded not guilty to an unrelated assault charge after arriving late for court Thursday.

Justin DiPietro, 26, was initially absent from court, leading to the threat of an arrest warrant. Reporters had left by the time he arrived later to enter his plea.

DiPietro was arrested July 6 for allegedly assaulting a former girlfriend in Portland, but was out on bail.

The disappearance of Ayla Reynolds remains unsolved. DiPietro reported her missing Dec. 17, 2011, from his mother’s home in Waterville.

Ayla was 20 months old, and police say she’s presumed to be dead. Police have called the case the biggest criminal investigation in Maine history.

As for the assault charge, police said DiPietro grabbed and pushed Courtney Roberts while the two were arguing. The original $200 bail and requirement that DiPietro stay away from Roberts remain in place.

DiPietro couldn’t be reached Thursday after the hearing. A lawyer who has represented some of his family members didn’t immediately return a phone call seeking comment.