PAUL Farmer, an American physician and medical anthropologist renowned for his innovative work in providing health care to poorer countries including Lesotho, died Monday at age 62, his Partners in Health group said.

The Boston-based organisation said Dr Farmer "unexpectedly passed away in his sleep while in Rwanda."

Farmer's work on providing healthcare solutions to Lesotho and other countries like Rwanda, Haiti, Kazakhstan, Liberia, Malawi, Mexico, Peru, Russia and Sierra Leone brought him wide acclaim.

A 2003 book profiling him, "Mountains Beyond Mountains," called him "the man who would cure the world."

Samantha Power, the former US ambassador to the United Nations, tweeted that Farmer was "a giant" in his field.

"Devastating news," she posted. "Paul Farmer gave everything -- everything -- to others. He saw the worst, and yet did all he could to bring out the best in everyone he encountered."

Pulmonologist and medical analyst Dr Vin Gupta tweeted: "It is hard to overstate the impact Dr Paul Farmer had on the medical profession."

And actor Edward Norton, a social and environmental activist, called Farmer "one of the most loving, funny, generous & inspiring people to grace humanity with his soul in our lifetimes."

Working in Haiti in 1987, Farmer co-founded Partners in Health to help devise and deliver better healthcare in poor and badly underserved countries.

A co-founder and close longtime associate was Jim Yong Kim, who went on to lead the World Bank from 2012 to 2019.

In 2009, Farmer succeeded Kim as chair of the Department of Global Health and Social Medicine at Harvard Medical School.

The same year he was named a UN deputy special envoy to Haiti, working with Bill Clinton.

Farmer held that position at the time of the island's devastating 2010 earthquake, and soon was headed to Haiti on an airplane full of physicians.

Farmer, a lifelong advocate for the poor Caribbean nation, co-founded the Institute for Justice and Democracy in Haiti.