"On behalf of all of us, to congratulate Iranian film director Asghar Farhadi on his Oscar win," told reporters at a briefing.
The film was honoured at the 84th Academy Awards ceremony in Los Angeles Sunday night, Xinhua reported.
State Department spokeswoman Victoria Nuland said the film, first Iranian film to win Oscar, "really gives the world an invaluable picture of life in Iran".
"We applaud his achievement and celebrate the vibrancy and historical greatness of the independent film industry in Iran," Nuland told reporters.
"Children of Heaven" in 1998 was the only other Iranian film which had been nominated for Best Foreign Language Film.
The widely-hailed movie also won the best foreign film at the Golden Globes.