NAIROBI (Reuters) - Unknown attackers torched a car belonging to deputy head of the parliament of Comoros late on Sunday, the latest in a series of threats apparently aimed at derailing an investigation he is leading, the lawmaker said. Dhoulkamal Dhoihir, vice president of the National Assembly, is leading an inquiry into a plan to sell Comoros citizenship to stateless people in Gulf states. The scheme would earn Comoros, an island state off Africa s eastern coast, $200 million to $300 million, but it has been dogged by allegations of corruption. The incident comes a day before the commission Dhoihir heads is due to question two former presidents - Ikililou Dhoinine, who left office last year, and Ahmed Abdallah Mohamed Sambi, who launched the citizenship scheme in late 2008.  As I was finishing up my dinner I heard a loud noise and the car alarm go off. I opened the door and saw my car on fire. Everything was destroyed,  Dhoihir told Reuters on Monday.  It was definitely linked to my work. There are lots of people who don t want this information to come out,  he added. Abdoul-Kader Mahmoud, the director of the police, said the investigation was continuing, but officers had not yet identified the cause of the incident.  It could have been a technical problem, but we are not ruling out any explanation,  he told Reuters. Dhoirir said that he had faced threats via social media and a group of MPs have tried to shut down his commission of inquiry, which began work in the summer and is due to submit its report next month. Dhoirir said that the commission had requested extra security after coming under increased pressure as the investigation advanced. None was provided until Sunday night, after the fire, he said. Mahmoud denied commissioners had requested extra security before the incident but said officers had been dispatched to the residences of members of the commission.  We have taken the measures. We have sent more men to protect these people,  he said. Under President Azali Assoumani, the Comoros government has suspended the issuing of new citizenships until the commission completes its work.  This is a very serious incident. Those who risk being exposed are sending a very clear message,  a former top government official said. 