The source told Lusa that the death is thought to have been from "natural causes ".
Tazi, 65, has been in Monsanto jail since 23 March 2017, when he was first remanded into custody. He was later convicted of seven crimes: forgery with a view to terrorism, recruiing for terrorism, financing of terrorism, and four crimes of using false documents with a view to financing terrorism.
On 9 July 2019 the Lisbon Central Criminal Court sentenced him to a single sentence of 12 years in prison for seven of the eight crimes with which he was charged, while acquitting him of being a member of an international terrorist organisation.
His lawyer, Lopes Guerreiro, lodged an appeal against the verdict to the Lisbon Court of Appeal. The decision was expected to be made known on the afternoon of Wednesday, 8 January, but a court source told Lusa that day that the ruling on the appeal had been "postponed" to 22 January.