CAIRO (TIP): The knock on the door came just before midnight, a group of plainclothes police demanding that 29-year-old Fatma el-Sayed, an activist with one of Egypt‘s secular opposition groups, come with them. Her father pleaded to accompany her, but they took her away, alone.

For the next four days, el-Sayed was kept in a cell in the security agency headquarters in her home town of Alexandria — off official records, essentially disappeared into Egypt’s labyrinth of detention facilities. She was interrogated without a lawyer and denied the injections she needed after recent surgery.

“They tried to extract information from me,” she said — about fellow activists in the opposition group April 6, about the group’s call for a protest against the high cost of living, about any coordination with the Muslim Brotherhood.

“I gave them nothing,” she said.

Egyptian security agencies are increasingly detaining activists and students in secret, snatching them from homes or the street and holding them without official record of their arrest, as their families scramble to find them, activists and lawyers say.

Activists have tracked more than 160 such suspected disappearances in police custody during the past two months — a sign of the renewed unchecked power of security agencies. It is a return to past practices under autocratic leader Hosni Mubarak, when detainees were held, sometimes for years, without trial under notorious emergency laws in effect for decades and lifted after his 2011 ouster.

El-Sayed was lucky. After four days, police filed a record of her arrest and released her on bail. She has been charged with membership in April 6, a leading force in the anti-Mubarak uprising that is now banned. Other missing activists have reappeared days or even weeks later when police finally filed arrest reports.

But the whereabouts of most remains unknown. Activists and lawyers fear they are abused during interrogation.

At least one of the missing turned up dead. Islam Ateto was taken by security agents in May as he left a classroom at a Cairo university, according to student unions. Soon after, police announced that Ateto was killed in a gunbattle with security forces in the desert, alleging he was wanted for the assassination of a police officer.

Government officials, including Prime Minister Ibrahim Mahlab, have repeatedly denied there are any extra-legal detainees in Egypt, saying those in custody are held either on a prosecutor’s order or were arrested during the act of a crime. With the recent spike in reports of missing detainees, government officials have largely ignored calls for an explanation. Repeated requests by The Associated Press to the spokesman for the Interior Ministry received no response. A senior security official dismissed allegations of disappearances and questioned how it could be proven that security agents took anyone away.

However, another official said secret interrogations and detention were sometimes necessary when state security or intelligence agencies are pursuing terror cells that threaten national security. Both officials spoke on condition of anonymity because they were not permitted to speak to the media. The government has repeatedly touted its “war on terrorism” — a reference to its battle against Islamic militants carrying out stepped-up attacks and to a crackdown on Islamists following the military’s July 2013 ouster of Islamist President Mohammed Morsi. With the clampdown, many activists have gone into hiding, complicating efforts to determine who has been detained.

When grilled by the father of a missing woman on a private television station last week, Interior Ministry spokesman Abu Bakr Abdel-Karim insisted that if she had been arrested, “legal procedures must have been followed.” The woman, Esraa el-Taweel, a 23-year old freelance photojournalist, was reported by her family to have been snatched on June 1 from a street in downtown Cairo, along with two male friends. Later, inmates got word to relatives that they had seen the two friends in a prison.

El-Taweel finally surfaced Wednesday, when a visitor spotted her at a women’s prison near Cairo. On Thursday, she was brought for questioning before State Security prosecutors, who usually deal with terrorism cases, the first official acknowledgement of her detention.

Lawyers say Islamists were frequently the targets of secret detentions over the past two years, and now the practice is increasingly being used against more secular activists.

One activist group, Freedom for the Brave, has documented more than 160 cases since April. Of those, 66 have resurfaced.

The Egyptian Coordination of Rights and Freedoms, a group of lawyers tracking missing suspected Brotherhood members, has recorded more than 210 cases as of May; one person has been missing since 2013.

The London-based Human Rights Monitor recorded 31 cases of disappearance in May alone, in addition to 13 others from the two previous months. The group reported the cases to the U.N Working Group on Enforced Disappearance, which usually follows up on such reports.

The National Human Rights Council, whose members are appointed by the state, has submitted 71 reported cases of missing people to the Interior Ministry and prosecutors’ office, said council member Nasser Amin. “In Egypt, there are plenty of cases of illegal detention,” a crime punishable by up to seven years in prison, he said. The council is working to determine if any missing cases reach the level of “enforced disappearance,” a crime against humanity under international law that involves a long period of disappearance, proof of an active government role and an exhaustive investigation to find the missing person. Amin said the United Nations has designated 13 cases of people missing since the turmoil in 2011 as likely enforced disappearances and has sought an explanation from the Egyptian government.