(Jerusalem) – Egyptian authorities should immediately disclose whether they are or were holding four Palestinian men from Gaza affiliated with Hamas whose whereabouts are unknown, Human Rights Watch said today in a letter to Interior Minister Magdy Abd al-Ghaffar. The Palestinians were taken away by armed men after crossing from Gaza to Egypt nearly 20 months ago.

Based on media reports, including photographs purporting to show two of the men in a Cairo detention facility, the families believe they are in Egyptian custody. If true, their prolonged incommunicado detention, with Egyptian authorities denying knowledge of the detention or refusing to reveal their whereabouts, would constitute enforced disappearances. Authorities should immediately charge the men if they suspect them of criminal activity, or otherwise release them.

“Twenty months without contact with the missing men inflicts incalculable anguish and suffering on their families and friends,” said Sarah Leah Whitson, Middle East director at Human Rights Watch. “Egyptian authorities should come clean and reveal whether these four disappeared Palestinian men from Gaza are in their custody.”

The men are Abdullah Abu al-Jebain, 23, from the Jabaliya refugee camp; Abd al-Dayyam Abu Lebda, 26, from the al-Bureij refugee camp; Hussein al-Zebda, 29, a resident of Sheikh Radwan; and Yasser Zenoun, 26, a resident of Rafah City. Their families told Human Rights Watch that the men legally passed through the Rafah crossing on August 19, 2015, calling them from the Egyptian side of the crossing that evening, and later that night boarded a bus headed to Cairo International Airport via the Sinai Peninsula.

The families said that the men were planning to head to Turkey – al-Jebain and Abu Lebda to continue their studies and al-Zebda and Zenoun to receive medical care. About 300 meters after the bus left Rafah, six armed men in civilian clothes fired on the bus and forcibly took custody of the four men, other passengers on the bus told the families. The families have not heard from the men since.

Al Jazeera published a photograph in August 2016 claiming to show two of the men, Abu Lebda and Zenoun, sitting in a Cairo detention facility. Several media outlets also have posted video footage purporting to show the two men in the same detention facility. The families of the two men say that the photographs and video do indeed show their relatives.

On August 20, 2015, the day after the men were abducted, Egyptian security officials and sources close to Hamas told Reuters that the four men were members of Hamas' armed wing. In September 2016, the Hamas then-Deputy Foreign Minister Ghazi Hamad told Human Rights Watch that all four men were Hamas members but not high-level officials. In August 2016, a Hamas official, Salah Bardawil, told the Shams News Agency that Egypt had set conditions for the men’s release, which reportedly include handing over a number of men wanted by the Egyptian authorities.

Human Rights Watch could not independently confirm these media accounts or the families’ information.

Egyptian authorities should immediately acknowledge whether any of the four men is in their custody, as government authorities are required to do under international law. This obligation is unconditional and cannot be contingent on the fulfillment of demands by the Gaza authorities. Egyptian authorities should immediately charge the men if they suspect them of criminal activity, or otherwise release them.

Incommunicado detention violates basic protections for both civilians and fighters under Egypt’s code of criminal procedure, which requires authorities to bring criminal suspects in front of a prosecutor within 24 hours and prosecutors to charge the detainee based on evidence or release the person immediately. It also violates international law, which requires that all detainees, regardless of their particular status, be brought “promptly” (i.e. within days) before a judicial officer or equivalent to review the legality and necessity of their detention.

Under international law, a country’s refusal to acknowledge that a person has been detained or to reveal a person’s whereabouts or fate following detention or arrest by government forces, placing the detainee outside the protection of the law, is an enforced disappearance. Enforced disappearance violates many of the rights guaranteed under the International Covenant on Civil and Political Rights, which Egypt ratified in 1982, including the requirement to bring detainees promptly before a judge. Enforced disappearances leave detainees exceptionally vulnerable to torture and other abuse. Under international law, countries must investigate enforced disappearances, hold anyone responsible to account, and properly compensate victims.

Detainees also have the right to humane treatment, communication with their families, access to counsel and the ability to challenge the basis for the detention, and visitation by the International Committee of the Red Cross.

Egyptian authorities have jailed tens of thousands of political opponents since the military’s removal of former President Mohamed Morsy in 2013. Between August 2015 and August 2016, the Egyptian Commission for Rights and Freedoms, an independent group, documented the enforced disappearance by the police of 912 people, 52 of whom had not reappeared by the time the group issued its report.