Pope Francis is urging residents of a mobster-plagued Rome suburb to be courageous and side with the law.

Francis celebrated an outdoor Mass on Sunday evening in Ostia, a seaside town. In his homily, he encouraged people to "knock down" the walls of social codes — known in Italy as "omerta" — that discourage people from denouncing mobsters.

In 2015, Ostia's municipal administration was put under Italian government control because of infiltration by local crime clans. Authorities have accused them of slayings, extortion, drug-trafficking and loan-sharking in Ostia.

The pope also decried abuse of power and arrogance, saying people must embrace "justice, decorum and lawfulness."

Journalists reporting on Ostia's mobsters have been physically threatened.

Francis called on people to shake off "fear and oppression."