JAKARTA (AFP) - A prominent Indonesian corruption investigator had acid thrown in his face by motorbike-riding assailants Tuesday (April 11) in an attack activists believe is linked to a graft case that has implicated senior politicians.

Novel Baswedan, a member of the official Corruption Eradication Commission (KPK), was being treated in hospital after the attack which happened in Jakarta as he walked home from a mosque in the early hours following morning prayers in the Muslim nation.

"It is a brutal act, I strongly condemn it," said President Joko Widodo, urging the police to track down the assailants.

Presidential spokesman Johan Budi, who visited Baswedan in hospital, gave details of the attack, telling AFP the investigator had injuries on his forehead and blurred vision in his left eye.

Anti-graft investigators in Indonesia, one of the world's most corrupt countries, have been targeted in the past and have reported having cars driven at them and receiving threats.

It was not immediately clear who was behind the latest assault but anti-graft NGO Indonesian Corruption Watch said they suspected it was linked to Baswedan's role in probing a corruption scandal that allegedly saw about US$170 million pilfered from government coffers.

The investigation is being led by the KPK.

Senior politicians, including the justice minister and ex-interior minister, have been implicated in the scandal, with investigators alleging they were among many who received kickbacks from funds earmarked for a government project to issue new ID cards.

Parliament speaker Setya Novanto, who has been implicated in the case, was late Monday hit with a six-month ban on travelling outside Indonesia, said immigration authorities. Such a step is usually taken in Indonesia when people are under investigation.

Indonesia was ranked 90th out of 176 countries and territories in Transparency International's Corruption Perceptions Index last year. A number one ranking represents the least corrupt.