RAMALLAH, July 12 (Xinhua) -- The death of former Palestinian leader Yasser Arafat was the result of an unknown poison, a Jordanian doctor who started an inquiry in the incident said Thursday. Arafats medical reports were unable to diagnose the disease, but indications suggest that he was poisoned by a toxic substance that was not examined at the time, said the doctor, Abdullah al- Basheer, in a news conference upon his arrival to the West Bank. Mahmoud Abbas, Arafats successor, ordered the investigation after Arab satellite channel al-Jazeera aired an investigative report concluding that Arafat was poisoned with radioactive polonium. To confirm al-Jazeeras report, Arafats body needs to be exhumed for further tests. The Palestinian leadership said it is ready to dig up Arafats remains for the investigation. Al-Basheer said the findings of the Lausanne-based Institute of Radiation Physics, which al-Jazeera used for testing Arafats personal belongings, were difficult to be conclusive due to the lack of previous examples of polonium poisoning. Arafat died at a French hospital near Paris, three weeks after he was airlifted from his West Bank headquarters, where he spent his last two years under an Israeli siege.