Warren worked to end the Balkans war and negotiated the release of American hostages in Iran [File: AFP]

Warren Christopher, a former US secretary of state who worked to end the war in Bosnia and negotiated the release of American hostages in Iran, has died, aged 85.

He "passed away peacefully, surrounded by family at his home in Los Angeles" of complications from kidney and bladder cancer, local media quoted his family as saying in a statement on Friday.

As the chief US statesman under former president Bill Clinton from 1993 to 1997, Christopher was a behind-the-scenes negotiator.

Often called the "stealth" secretary of state, he was known for his understated, self-effacing manner.

"Careful listening may be the secret weapon," the New York Times quoted him as saying in a 1981 speech when he was deputy secretary of state.

"I observed some time ago that I was better at listening than at talking."

That "secret weapon" helped Christopher weather diplomatic crises.

In 1995, he intervened during the crucial final days of the US-brokered Bosnian peace talks at Dayton, Ohio. He had an important role in closing the deal, according to his then deputy, Richard Holbrooke, the force behind the agreement.

As secretary of state, Christopher devoted much of his time to the Middle East. He made at least 18 trips to the region in pursuit of peace and a ceasefire in southern Lebanon between Israel and Hezbollah.

In 1994, he witnessed the signing of a peace treaty between Jordan and Israel.

As Jimmy Carter's deputy secretary of state, he negotiated the release of 52 Americans taken hostage at the US embassy in Tehran in 1979. The hostages were freed on January 20, 1981, minutes after Ronald Reagan was sworn in to succeed Carter as president.

He also helped negotiate the Panama Canal treaty, worked on establishing normal relations with China and played a major role in developing Carter's human-rights policies.