A Mexican judge has ruled there is insufficient evidence to try four of seven soldiers charged with killing 22 suspects after they surrendered.

But the officer and three soldiers will still face lesser charges.

The army had said the suspects were members of a drug gang and died in a gun battle near the village of San Pedro Limon in Mexico state in 2014.

The judge ruled there was evidence to continue the trials of three soldiers who allegedly carried out the killings. The four soldiers against whom the main charges were dropped will also face military charges connected to violating the rules of engagement and so will remain in prison for the time being. The government human rights commission said that the bodies of 15 of the 22 people who died in the confrontation with the army had shown signs that they were apparently shot after they surrendered.

Several of the victims had defensive wounds, suggesting they were shot while unarmed.

Witnesses in the case said they had been threatened and tortured to try to get them to change their versions and seven state police officers were accused by the authorities of torturing three witnesses.