Reuters reported that Israeli Foreign Minister Eli Cohen sent letters of appeal after Gaza's ruling Palestinian group Hamas released a video of captive Avera Mengistu, who walked into the enclave and whose family says he has a mental illness.

Another Israeli civilian is being held in Gaza after entering under similar circumstances in 2015, as are two Israeli soldiers who went missing during a war with Hamas in 2014 and were declared dead by the army.

Cohen described Mengistu's plight as "a gross violation of international humanitarian law, with no information on his health condition nor means of communication with family nor Red Cross visits," the Foreign Ministry said.

Hamas's release of the video on Monday appeared to be an effort to pressure Israel into a prisoner swap. Israel has said it explored indirect talks with Hamas on recovering the four without specifying what it might give in return.

Meanwhile, the Israeli Broadcasting Authority (Kan) said that the Hamas movement is intensifying its efforts to kidnap Israeli soldiers on the borders of the Gaza Strip, to promote an exchange deal with Israel.

Kan said Hamas is trying to step up kidnapping attempts after it realized the Israeli prisoners it has were not a powerful bargaining chip to implement an exchange similar to the 2011 Shalit deal.

The channel accused Hamas politburo chief, Ismail Haniyeh, and his deputy, Saleh al-Arouri, who live abroad, of pushing the al-Qassam Brigades to kidnap soldiers.

According to what it reported, Hamas intended to surprise the army and carry out the kidnapping during the calm period, not during security tension or escalation.

The Israeli report came one day after Hamas warned Israel that the window to negotiate a prisoner deal is closing, and another way will be found.