Dos Santos, 79, has been receiving medical treatment since 2019, but his health deteriorated and he was admitted to an intensive care unit, Lusa reported on Thursday, without saying when this occurred.
One of Africa's longest serving leaders, dos Santos stepped down five years ago. His rule was marked by a brutal civil war lasting nearly three decades against U.S.-backed UNITA rebels - which he won in 2002 - and a subsequent oil-fuel
Dos Santos was replaced in 2017 by President Joao Lourenco, who despite being from the incumbent's People's Movement for the Liberation of Angola (MPLA), swiftly moved to probe allegations of multi-billion dollar corruption during the dos Santos era, targeting the former leader's children.
Last year dos Santos returned home for the first time since he went into exile in Barcelona in April 2019.
The Angolan government did not respond immediately on Friday to a request for comment on the former president's condition.
