The protests are the latest since parliament approved the amendment of a law last week to allow members of the military to hold more government roles -- which critics said would expand military authority over civilian affairs.

Hundreds of protesters, many dressed in black and brandishing banners that said "Reject militarism" gathered near parliament. Others called for the soldiers to be sent "back to the barracks".

Demonstrations began peacefully. But when protesters tried to breach the fence surrounding parliament, hurling petrol bombs and firecrackers inside, security forces moved in to blast the crowd with water cannons.

"The passing of the armed forces law will open the way for the military to hold civilian posts", said 20-year-old Sarah, a protester who gave only her first name. "It will also shrink civilian space".

Protests since the law was passed have rocked several cities.

On Monday, police in Surabaya in East Java also used water cannons to break up the crowds after protesters hurled rocks, sticks and Molotov cocktails.

The March 20 revision to the armed forces law, pushed mainly by President Prabowo Subianto's coalition, was aimed at expanding the military's role beyond defense in a country long influenced by its powerful armed forces. 

The new law allows active military officers to hold a position in 14 government institutions without resigning, an increase from 10 institutions in the previous law. 

The amendment has sparked fears of a return to the era of late dictator Suharto, under whom Prabowo, an ex-general, once served -- and which saw the military used to crack down on dissent.

Rights groups have said the change would enable officials to fill more civilian posts with active-duty military personnel and weaken legal checks on abusive officials.