John Gunther Dean, the US ambassador who famously carried the American flag to a helicopter leaving Phnom Penh as the capital fell to the Khmer Rouge in 1975, has died at the age of 93.

His wife and children announced his passing on Thursday in an obituary posted online.

His granddaughter Laura Dean said the exact cause of his death was not immediately known, the Washington Post reported.

Years after his departure from Cambodia, Dean spoke of his sorrow at failing to rescue more Cambodians from the horrors of the ultra-Maoist regime.

“I failed. I tried so hard. I took as many people as I could, hundreds of them, I took them out, but I couldn’t take the whole nation out,” Dean told the Associated Press (AP) in an interview in 2015 from Paris, where he mainly lived after retiring.

He also spoke of his shame at the US “walking out” on Cambodia without keeping its promises to the Kingdom in the interview commemorating the 40th anniversary of the fall of Phnom Penh on April 17, 1975.

A photograph of him carrying the embassy’s flag in a plastic bag to a departing helicopter became one of the iconic images of the Vietnam War period.

“We’d accepted responsibility for Cambodia and then walked out without fulfilling our promise. That’s the worst thing a country can do. And I cried because I knew what was going to happen,” Dean said in the AP interview.

Dean oversaw the evacuation of the US embassy, frantically trying organise flight from the encircling Khmer Rouge.

One Cambodian official, Prince Sisowath Sirik Matak, wrote to Dean to refuse his offer of escape.

“I thank you very sincerely . . . for your offer to transport me towards freedom. I cannot, alas, leave in such a cowardly fashion.

“As for you and in particular for your great country, I never believed for a moment that you would have this sentiment of abandoning a people which has chosen liberty. You have refused us your protection and we can do nothing about it.

“I have only committed the mistake of believing in you, the Americans,” Sirik Matak wrote.

The former deputy prime minister was likely executed by the Khmer Rouge a week after the fall of Phnom Penh.

Dean described the letter to AP as the “greatest accusation ever made by foreigners. It is wrenching, no? And put yourself in the role of the American representative”.

Dean was later ambassador to Denmark, Lebanon and Thailand. His final posting was in India from 1985-89. He served under four US presidents.

“He was a skilled diplomat that championed strong US-India relations. Rest in peace and you will be forever missed,” the US embassy in India tweeted.

Born in Germany in 1926, his Jewish family moved to the US in 1938 to escape Nazism.

Dean, who spoke English, French, German, and Danish, is survived by his French-born wife Martine and three children.