Jakarta – A small bomb exploded outside the house of anti-corruption activist on the Indonesian island of Sulawesi early on Tuesday, breaking windows but causing no injuries, police said.

The bomb – the second attack on the home the activist Hidayatullah in the past year – exploded at 3.30am in the town of Kendari, about 1,740km northeast of the capital Jakarta. "The explosion came from a rudimentary low explosive device, and we are investigating the motive," said local police.

No one has been arrested but some police officials believe the attack was in response to Hidayatullah's campaign against corruption in the local parliament. His group, the People's Mandate Assembly, have repeatedly held protests against authorities' failure to detain corrupt legislators.

Indonesia is considered one of the world's most corrupt countries and graft is widespread in most government institutions. But in recent months, prosecutors have begun charging dozens of local politicians with corruption in a campaign to clean up local and regional governments.