One of the aides to the late Egyptian president and his son has been detained illegally since 2013, as part of the political persecution of former Morsi aides, and should be immediately released and compensated, human rights experts say.

The UN Working Group on Arbitrary Detention published its findings last week, after examining the cases of Issam al-Haddad (a Morsi aide) and his son Jihad. The committee said the Egyptian authorities did not respond to the working group's questions.

A Cairo court overturned a life sentence for spying on Issam and Jihad in 2016, according to a statement issued by the support group.

Haddad during a previous meeting with President Morsi (Reuters)

After a retrial this year, they were acquitted last September, but Issam was sentenced to 10 years in prison for joining a banned group, while the same charges were immediately brought against Jihad, who remains in custody.

The UN commission said in a review that the case of mourning "appears to be consistent with the pattern of systematic, widespread and crude violations of fundamental human rights directed against prominent figures in the government of Mohamed Morsi, whose supporters have been ousted or perceived to be their supporters."

"They are deprived of their liberty arbitrarily," she said, appealing to the Egyptian authorities to respond within six months to complaints contained in her findings. "Their trials should never have taken place," she said.

The committee said the trial of Essam and his son under the anti-terrorism law for joining the Muslim Brotherhood, which banned its activities in 2013 and then designated a terrorist group, "is incompatible with the concept of justice," as they had previously been held.