The body of Libya's former oil minister Shukri Ghanem, who had defected from Moamer Kadhafi's regime, was found Sunday in the Danube, Austrian police said in a statement.
No trace of violence was found on the body, police spokesman Roman Hahslinger said, adding that "it is possible that he felt unwell and fell into the water".
An autopsy will be carried out to determine the cause of death.
Earlier, APA news agency had reported that Ghanem, 69, was found dead in his apartment after having apparently suffered from a heart attack.
The news agency based its report on an Islamic expert, Amer al-Bayati, who was in turn citing Ghanem's family.
Ghanem served as Libya's oil minister from 2006 to 2011.
At the height of the crisis in Libya, he crossed over to neighbouring Tunisia in mid-May 2011, by car and became one of the highest-ranking officials to defect from the regime.
His defection came just weeks before he was due to represent Libya at an Organisation of Petroleum Exporting Countries meeting in Vienna.
In June, he announced his defection through Italian news agency ANSA, saying he left his home country to "to join the choice made by young Libyans to fight for a democratic country".
However, Ghanem added that he was not working with the National Transitional Council, which is Libya's current interim government.
Instead, he sought refuge in Vienna, a city he knows well having not only travelled there regularly as oil minister for OPEC meetings, but also having lived there when he was director of OPEC's research division from 1993 to 2001.
He later returned to Libya where he was economy minister, before being named prime minister in June 2003.
In 2006, as he took over the oil minister portfolio, he was also appointed chairman of the National Oil Corporation.
Ghanem's funeral may be held in Libya, APA said, quoting Bayati.