A mob opposed to public discussion of Indonesia’s 1965 massacre of communists tried to force its way into a building where they believed communists were meeting, injuring five policemen.

Jakarta police spokesman Argo Yuwono said 22 people were arrested on Monday for rioting and five officers were injured in the confrontation.

The melee came after police blockaded the building on Saturday to stop a public forum on the massacre, in which historians say half a million people were killed, from going ahead.

Indonesia held a ground-breaking symposium on the massacre last year, breaking a half century of near silence on the issue, but the military, Islamic groups and many in the government are opposed to unearthing the truth, saying it could revive communism.