Kurt Waldheim, former Secretary General of the United Nations and Austrian president whose image was later tarnished by his unproved involvement in Nazi war atrocities, died on Thursday at the age of 88.

Waldheim died of heart failure, with his family at his bedside, the Austrian APA news agency said, quoting Waldheim's son-in-law.

The former statesman was hospitalized for infection and fever in Vienna last month, but he left the hospital last week.

After Waldheim's death, Austrian President Heinz Fischer issued a statement expressing his "deepest condolences," and the flag outside his office was flying at half-staff Thursday afternoon.

Waldheim served as UN chief for two consecutive tenures from 1972 to 1981, and was elected Austrian president in 1986.

During his service in the UN, Waldheim was credited with his efforts to promote peace in the Middle East.

His political career was tainted by a cover-up of his service in the German army in World War II, although he denied involvement in any wrongdoing.

Following the disclosure of his controversial past when he was running for the Austrian presidency, Waldheim was banned by the U.S. government from visiting the United States.

In 1988, an international investigative group consisting of six historians issued a report clearing him of personal involvement in wartime atrocities, but claimed that he was aware of those crimes.

Although his credit largely remained unaffected at home, the former president was unpopular abroad and made almost no state visits while in office.

Kurt Waldheim was born in St. Andrae-Woerdern, a village near Vienna, on Dec. 21, 1918. His father was a local school inspector, who married a daughter of the mayor.

Waldheim devoted his most lifetime to politics. He joined the Austrian diplomatic service in 1945, after finishing his studies in law at the University of Vienna.

Editor: Yan