Three teachers from a total of seven suspects in the gang rape case against an underage girl at a school in Mukdahan province are likely to face charges for sexually assaulting another 16-year-old student.

The three teachers are Wipoj Saensuk, Anupap Banjong and Yutthana Phuthanonnok.

The teachers have been accused of organising the gang rape and asked others to join in, police said.

The 16-year-old victim, a student at the same school, is serving as a witness in the first gang rape case against a 14-year-old girl.

The teenager said she had been raped by some of the men accused in the other case and the information she had provided corroborated that given by the first victim.

Both victims were reportedly raped on a number of occasions over a one-year period starting in March 2019.

The alleged gang rape case sparked national outrage when the grandmother of the 14-year-old girl filed a criminal complaint last week.

So far, police had pressed charges against five teachers and two male alumni. All have denied the charges against them.

Meanwhile, police investigators searched four sites connected with the alleged crimes -- the school gym, the volleyball court, the teacher rooms and their private residences.

Police found used condoms and a number of empty liquor bottles.