Medan – Indonesia's army chief dishonourably discharged 20 soldiers from a crack airborne unit on Wednesday, saying they had behaved like thugs by killing at least seven people in recent attacks on two police posts.

Over the weekend and on Monday, around 100 soldiers armed with rifles and grenades attacked the police stations at Binjai town in north Sumatra after a soldier was arrested for suspected drugs offences.

"You've acted out of control. You've acted with arrogance. You've acted like thugs ... You have violated your own oath to the corps, army and this country," Army Chief of Staff Ryamizard Ryacudu said as he addressed Airborne Battalion 100.

"We regret the incident happened and I take this chance to again apologise to the families of the victims," he added in a speech made at the North Sumatra military headquarters in the local capital Medan, 1,450 km northwest of Jakarta.

The army chief also took five officers from the battalion off active duty while the military continued its investigations into the incident, although it was unclear whether those soldiers discharged would now face police investigation.

Several soldiers first attacked the Binjai police posts late last Saturday, but the worst violence occurred early on Monday when at least seven people, including five police were killed, and around 15 wounded.

The deadly incident underscores the poor discipline among the branches of Indonesia's security forces in the field. In conflict zones, there are occasional armed clashes between police and soldiers, often over petty disputes.