Bill Richardson, a veteran Democratic politician and former US ambassador to the United Nations who later spent decades negotiating the release of Americans detained around the world, has died at age 75, his associates said Saturday.

Richardson, who also served as governor of New Mexico and the US energy secretary, "passed away peacefully in his sleep" on Friday night, the Richardson Center for Global Engagement said in a statement.

Richardson was one of the highest-profile Latinos in the US political world. He made his name as the Indiana Jones of US diplomacy and was famed for daring head-to-head encounters with strongmen leaders on the US pariah list, including Iraq's late president Saddam Hussein and Cuba's late leader Fidel Castro.

More recently he was involved in efforts that led to the release of US basketball star Brittney Griner from a Russian prison after she was convicted of a drug offense. 

The statement from the Richardson Center said, "He lived his entire life in the service of others – including both his time in government and his subsequent career helping to free people held hostage or wrongfully detained abroad."

It added: "There was no person that Governor Richardson would not speak with if it held the promise of returning a person to freedom."