When the victim's family raised an alarm, the suspects drove the ambulance away. (Representational)

Two men have been arrested for their alleged involvement in a suspected sexual assault of a Sikh teenage girl inside an ambulance in Pakistan's Punjab province, Dawn newspaper reported on Monday.

The 15-year-old girl, said to be mentally unstable, had gone missing at midnight on Saturday from her home in Nankana Sahib city, some 80 km from Lahore, the police said.

The family looked for her everywhere but could not trace her. The girl's father said they spotted an ambulance of the Punjab Emergency Services Rescue 1122 parked at Nankana bypass.

On peeping inside, the family found that two men, identified as Ahsan Ali and Sameen Haider, were sexually assaulting their daughter, the Express Tribune reported.

According to a FIR registered by the police, when the victim's family raised an alarm, the suspects drove the ambulance away, threw out the victim near a sugar mill on Nankana Road and escaped.

A police spokesperson said the suspects were arrested.

District Emergency Officer Akram Panwaar told the daily that a high-level committee had been set up to investigate the incident. "Once the crime is proven, strong departmental action will be taken against the rescue workers."