Correction: March 24, 2016: A previous version of this article misidentified Zeid Ra'ad al-Hussein as the UNHCR Commissioner.

The UN's high commissioner for human rights has expressed "grave concern" over Egypt's prosecutions of human rights defenders and the shutdown of civil society organisations by the military government.

The comments from Zeid Ra'ad al-Hussein on Wednesday came ahead of a judicial hearing for two key human rights activists set to begin on Thursday in Cairo. Media outlets are restricted from reporting on the proceedings under a court order.

"This looks like a clampdown on sections of Egyptian civil society and it must stop," said Zeid. "NGOs who have played a valuable role in documenting violations and supporting victims will see their activities completely crippled if this continues. This will stifle the voices of those who advocate for victims."

Egypt's Sisi offers 'to sell himself'

A series of travel bans, interrogations, and asset freezes indicate that criminal charges may be pending against rights groups in the country, an alliance of international rights groups also warned on Wednesday.

Civil rights in Egypt have been increasingly restricted since President Abdel Fattah el-Sisi - then head of the armed forces - ousted president Mohammed Morsi in 2013.

International rights groups warned that leading Egyptian human rights defenders may face trial on charges of working without official registration, or accepting foreign funds without government authorisation.

The latter charge could carry sentences of life imprisonment under a decree issued by Sisi in 2014.

"The Egyptian authorities have moved beyond scaremongering and are now rapidly taking concrete steps to shut down the last critical voices in the country's human rights community," said Nadim Houry from New York-based Human Rights Watch.

The Egyptian Institute for Personal Rights, the Arab Network for Human Rights Information, and other local rights groups say the "independent human rights community in Egypt is at unprecedented risk".

London-based Amnesty International condemned Egypt's crackdown on human rights advocates, saying authorities should halt their "persecution" and drop attempts to prosecute them and seize their assets.

"Egypt's civil society is being treated like an enemy of the state rather than a partner for reform and progress," Amnesty's Said Boumedouha said.