A Jordanian man serving three years for supporting Islamic State extremists has died in custody, and his family blames medical neglect.

Yasser Idreis says his brother Nasser could have lived had he been treated sooner for a liver infection. Nasser Idreis died of cirrhosis Saturday in a Jordanian hospital and was buried in a desert cemetery Sunday near his hometown of Zarqa.

Security services spokesman Amer Sartawi denied the allegations, saying that "we did everything possible in treating the prisoner."

Jordan has been cracking down on IS supporters, with courts issuing sentences of several years for promoting the group. Hundreds of sympathizers have been imprisoned.

Impoverished Zarqa, a city with high unemployment, is a stronghold of jihadi Salafism, the ideology that spawned the al-Qaida terror network and Islamic State.