In an unusual move, Amnesty International called on activists Monday to contact leaders of the Hamas terror group to pressure them to free two Israeli citizens held in the Gaza Strip.

The human rights organization circulated a letter with the email addresses and fax numbers of senior Hamas members in a campaign to free Avraham Abera Mengistu and Hisham al-Sayed, two Israeli men who crossed into Gaza of their own accord several years ago. It was the first time the group has publicly attacked Hamas, which controls the coastal enclave.

The letter was headed, “URGENT ACTION: Israel civilians abducted for more than 2 years.” Amnesty pointed out in the letter that the two suffer from “serious mental health disorders” and that the organization fears “that the two men are being held as hostages by Hamas’ military wing, the Izz ad-Din al-Qassam Brigades for a potential prisoner exchange.” The letter explained that Mengistu, an Ethiopian Jew, has been in Gaza since September 2014 and Sayed, a Bedouin Israeli, since April 20, 2015.

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The organization demanded information about the two from Hamas, and called on people to send messages before September 4 and to contact local “diplomatic representatives in your country to urge them to take action.” September 4 marks the conclusion of the Muslim festival of Eid al-Adha, but it is unclear what the significance of the date is to the human rights group.

The group did not write about a third Israeli man, Juma Ibrahim Abu Ghanima, whose presence in Gaza is unconfirmed. Amnesty also did not mention that the Islamist terror group holds the bodies of IDF soldiers Oron Shaul and Hadar Goldin, who the army determined were killed in action in the 2014 Gaza war.

The letter gave a fax number for Hamas leader Ismail Haniyeh and the email address and fax number of Hamas co-founder Mahmoud al-Zahar.

Earlier this month it was reported that Hamas had refused an Israeli offer to release some prisoners in exchange for video proof of the fate of the three Israelis, which came after Israel rejected Hamas’s demand that it free 55 prisoners rearrested following their release in the 2011 Gilad Shalit deal, in which over 1,000 Palestinian security prisoners were released in exchange for a captive Israeli soldier.