Kurt Waldheim, the former UN secretary general and president of Austria whose hidden complicity in Nazi war crimes was exposed late in his career, died Thursday in Vienna, Austrian media reported. He was 88. He died of heart failure, the state broadcaster ORF reported.

Although it was never proved that Waldheim himself committed atrocities during World War II, he was a lieutenant in army intelligence, attached to brutal German military units that executed thousands of Yugoslav partisans and civilians and deported thousands of Greek Jews to death camps from 1942 to 1944. Waldheim lied about his wartime service in the Balkans, maintaining that his military career ended in 1942 after he was wounded in a battle on the Russian front.

But more than four decades later, his assertions were disputed by witnesses, photographs, medals and commendations given to Waldheim, and by his own signature on documents linked to massacres and deportations.

Kurt Waldheim was born on Dec. 21, 1918, in St. Andrä-Wördern, a village near Vienna. His father, Walter, the son of an impoverished blacksmith, became the local school superintendent and married a daughter of the mayor.