Houthi rebels claim they have gained control of most of Yemen's capital Sanaa, a claim denied by forces loyal to the country's former President Ali Abdullah Saleh.
Mr Saleh allied with the Houthis in the years after he was ousted from power in 2011, and the support of his loyalist military units was key to helping the Houthis overrun the capital, Sanaa, in 2014, driving out Mr Hadi's government.
A senior official with Yemen's internationally-recognized government confirmed to The Associated Press that Saleh had been killed, sending video purportedly showing Saleh's body being carried away by a group of armed men chanting, "Allahu akbar".
Yemen expert Nadwa Dawsari, of non-profit Project on Middle East Democracy, said Saleh's killing could have grave consequnces for the country.
Al Arabiya quoted a source in Saleh's GPC party as saying he was killed by a sniper.
In May 2015, following Saudi-led coalition air raids on his home in Sanaa, Saleh officially announced for the first time the establishment of his alliance with the Houthis.
The Houthis' political office on December 2 accused Saleh of staging a "coup" against "an alliance he never believed in".
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Yemen has since been rocked by rebel infighting. Security forces reported at least 60 dead in the fighting.
The fighting in the capital of Sanaa caused residents to cower in their homes as explosions rocked the city overnight.
"Saleh's actions in Yemen, in working with his former opponents the Houthis, were complicating numerous efforts at resolving the conflict", Harrison Akins, a researcher with the Howard Baker Center, told Newsweek.
Al-Masirah stated that Saleh was killed while trying to flee the capital for Marib province. A Saudi-led alliance then waged a bloody war to reinstall him.
Yemen's war has killed more than 10,000 people since 2015, displaced more than two million people, and caused a cholera outbreak infecting almost one million people.
The Houthis had branded him a traitor for allegedly striking a deal with Saudi Arabia. Earlier on Sunday, the Houthi television service said on its website that a "cruise missile" had been launched "towards the Al-Barakah nuclear reactor" without providing any evidence, according to Reuters.