Forty global figures including Ban Ki-moon, Hillary Clinton and Bono published Wednesday a joint letter calling on Bangladesh to stop "unfair" attacks and harassment of Nobel laureate Muhammad Yunus.

Yunus is credited with lifting millions out of poverty with his pioneering micro-credit bank, but he has fallen out with Prime Minister Sheikh Hasina who has said he is "sucking blood" from the poor.

The anti-graft watchdog last year ordered a wide-ranging probe into firms Yunus chairs and Hasina has attacked him personally, blaming him for the World Bank pulling out from a bridge project that was mired in corruption allegations.

The letter signed by former UN chief Ban, former US secretary of state Clinton, U2 singer Bono, former US vice president Al Gore and others said that they had "deep concerns" about Yunus's "well-being" and ability to focus on his work.

"It is ... painful to see Prof. Yunus, a man of impeccable integrity, and his life's work unfairly attacked and repeatedly harassed and investigated by your government," they said in the letter, which was also published in the Washington Post newspaper.

There was no immediate comment from the government.

Bangladesh's state-run Anti-Corruption Commission is winding up its investigations into Yunus and his social business firms, a senior ACC official told AFP on condition of anonymity.

"We are analysing thousands of documents," he said.

Yunus, 82, who was awarded the Nobel Peace Prize in 2006, has seen his reputation at home tarnished by a labour dispute with Hasina, who critics accuse of becoming increasingly authoritarian.

He was forced from his position as Grameen Bank's managing director in 2011 in a move his supporters blamed on the conflict. His interests include a multi-billion dollar stake in the country's largest mobile phone operator.

The bridge near Dhaka was finally opened in June after years of construction delays, and Hasina took the occasion to say Yunus should be "dipped in a river" for jeopardising its completion.