US civil rights leader Reverend Joseph Lowery, a key ally of Martin Luther King, has died aged 98.

Born in 1921, Mr Lowery worked closely alongside leading figures in the civil rights movement such as King and Jesse Jackson.

He co-founded the Southern Christian Leadership Conference with Mr King and other black ministers in 1957 to fight segregation across the Southern US. He served for 20 years as its president before stepping down in 1998.

Mr Lowery was married to Evelyn Gibson Lowery - who shared his activism - for 63 years before her death in 2013.

The Lowery Institute, now known as the Joseph and Evelyn Lowery Institute for Justice & Human Rights, was founded in his honour in 2001 and he was a member of its board.

Mr Lowery continued working for racial equality into his 90s. He spoke against South African apartheid, sought better conditions in US jails, pushed for more economic opportunities for minorities, promoted AIDS education and railed against what he saw as government indifference toward the lower classes.

In 2009, Mr Lowery was chosen to speak at the inauguration of the country's first black president Barack Obama, and was later awarded the Presidential Medal of Freedom, the highest civilian award in the United States.

"Our beloved, Rev Dr Joseph Echols Lowery, made his transition peacefully at home at 10pm on Friday, 27 March at the age of 98. He was surrounded by his daughters," Mr Lowery's family said.

"Reverend Joseph Lowery was a fighter for civil rights," said fellow civil rights leader Congressman John Lewis.

"He spoke up, spoke out, he never gave up. He marched and he protested all across America. We mourn his passing this evening."