CAIRO (Reuters) - Egypt revealed on Thursday that it was holding the daughter of Muslim Brotherhood leader Khairat al-Shater and five other people, three weeks after family members say they disappeared in a new government crackdown.

The state security prosecutor ordered Aisha al-Shater and the other five to be held for 15 days pending an investigation on charges including membership in a terrorist organization, state news agency MENA said.

Human Rights Watch said on Sunday that Egyptian police and security forces had conducted a mass arrest campaign, rounding up at least 40 political activists, lawyers and human rights workers since late October.

Security forces carrying out the arrests presented no warrants, and families were not told where the detainees were being held, the New York-based rights watchdog said.

Among the others whose detentions were revealed on Thursday along with Shater was Hoda Abd al-Moneim, a 60-year-old lawyer and Brotherhood member. Her family said in a statement they saw her early on Thursday at the state security prosecution office “after 21 days of enforced disappearance by the Egyptian authorities”.

Her daughters were “shocked to find that Hoda, a 60-year old mother and grandmother, was in a dire health condition with clear signs of weight loss, psychological trauma, severe signs of instability and shock,” the statement said. “She couldn’t give a reason for her condition to her family members.”

The interior ministry was not immediately available to comment.

Abd al-Moneim’s daughter Gihad Badawy told Reuters earlier this month that security forces took her mother away without presenting an arrest warrant, and that the family had no idea where she was being held.

The lawyer had previously had a blood clot in her leg but was not allowed to bring her medicine with her when she was detained.

The six people will now be held in custody for the next 15 days. After that, they could either be held longer or released.

The Brotherhood, a decades-old Islamist political movement with a mass following, won the first free elections after the 2011 uprising that ended autocrat Hosni Mubarak’s 30-year rule, but was toppled by the army after a year in power.

Since then, the group has been banned and hundreds of its followers have been jailed. The Brotherhood says it is a non-violent movement and denies any relationship to violent insurgencies waged by al Qaeda and Islamic State militants.

President Abdel Fattah al-Sisi’s supporters say a government crackdown on his opponents aims to keep Egypt stable after years of political and economic turmoil following the 2011 revolt.