Palestinian militant group Hamas has released a video appearing to show an Israeli citizen being held captive in the Gaza Strip.
The clip appears to show Hisham al-Sayed lying in a bed looking dazed and wearing an oxygen mask - the first sighting of him since 2015.
Israeli Prime Minister Naftali Bennett said releasing a video of a sick man was "reprehensible and desperate."
The BBC has not been able to independently verify the footage.
Hamas alleges that Mr al-Sayed is an Israeli soldier, but both the Israeli government and his family say he is a civilian with mental health problems.
The charity Human Rights Watch, which has criticised Mr al-Sayed's "unlawful detention" in the past, says he was last seen walking into the Gaza Strip in April 2015 for unknown reasons, having made similar attempts to cross the frontier in the past.
In the video released by Hamas the 34-year-old, who is a member of Israel's Bedouin Arab minority, could be seen lying attached to a ventilator beside what appeared to be his Israeli-issued ID card.
A television monitor also in the room showed news footage from an economic conference in Qatar earlier this month.
No further details were given by the Palestinian militant group about the detainee's condition other than a reference on Monday to his health having deteriorated.
Israel says he is one of two citizens, the second being Avera Mengistu, currently being held captive by Hamas in violation of international law.
Both are believed to have crossed willingly into the Gaza Strip despite Israel banning its citizens from entering the Palestinian enclave.
There was some suggestion that the video's release was an attempt by Hamas to pressure Israel into resuming prisoner swap negotiations.
The two sides have engaged in prisoner swaps in the past, most notably in 2011 when abducted Israeli soldier Gilad Shalit was released in exchange for more than 1,000 Palestinians held in Israeli jails.