An Egyptian activist group said on Monday it was concerned for the health of Mohamed Sultan, a detained Egyptian-American who has been on hunger strike for 233 days.

Freedom for the Brave – a grassroots movement calling for the release of political detainees in Egypt – said a prison official had told Sultan’s mother and a US embassy representative that Sultan could not meet them due to his deteriorating condition.

“We are very concerned for [Sultan’s] health and we call on all human rights organisations in Egypt to urge the authorities to release him and to hold them fully responsible in the event of his death,” the group’s statement said.

Sultan’s family requested reviewing Sultan’s medical records during the attempted visit, but, according to the statement, officials refused.

Sultan is currently in a prison hospital.

He is detained pending trial with 50 others – including Muslim Brotherhood Supreme Guide Mohamed Badie – in the so-called “Rabaa control room” case.

They are accused of setting up an operation room after the violent dispersal of the pro-Mohamed Morsi Rabaa Al-Adawiya protest camp in mid-August 2013, as part of plans to defy the state and spread chaos, as well as plot attacks on police stations, private property and churches.

Sultan, 26, was arrested following the Rabaa dispersal. His family claims that he was not involved in politics and had returned to Egypt to care for his sick mother.

His father, Saleh Sultan, a leading Islamic preacher and a member of the National Alliance to Support Legitimacy – a group opposing president Mohamed Morsi’s ouster – was rounded up by authorities in a crackdown on Morsi sympathisers.

Sultan's family has already launched a campaign in Egypt as well as the US to call for his release.

Meanwhile, at least 80 people in Egyptian jails are on hunger strike against their detention and the protest law, which was issued last November and is deemed too restrictive. Hundreds have been arrested under its provisions.

In addition, a solidarity hunger strike has been launched in recent days by at least 200 others, including families of the detainees, activists and journalists.