Iran has extended the temporary prison release of a US citizen freed earlier this week, his brother said Saturday, voicing hopes the liberation would become permanent.

Siamak Namazi, a 51-year-old Iranian-American, has been held in Iran for years along with his elderly father, former UNICEF official Baquer Namazi, under convictions for espionage, allegations they both deny.

The younger Namazi was granted release from prison after his father, who was serving his sentence under house arrest, was allowed to travel to Abu Dhabi for medical treatment.

Siamak's brother, Babak Namazi, said in a statement Saturday that Iranian authorities had granted his sibling a further three-day furlough and that he hoped a longer extension would follow.

"We hope and pray that he will be granted his full freedom soon so that our family can finally be made whole again," wrote Babak.

He added that his father -- counter to the recommendations of his Iranian physicians -- would not undergo surgery for now to clear a life-threatening blockage in his left carotid artery.

Baquer Namazi will instead attempt alternative treatments recommended by the Abu Dhabi medical team.

His release comes as Iran's clerical state faces new sanctions for cracking down on major protests triggered by the death in custody of Mahsa Amini, a young woman accused of violating rules on covering her hair.

At least two other American citizens are held in Iran.