JERUSALEM — Hamas, the Islamic militant group that controls Gaza, released a video on Monday with footage of a man who identified himself as Avera Mengistu, an Israeli civilian held captive by the Palestinian group since 2014, issuing a direct challenge to Israel’s incoming military chief of staff and its new hard-line government.
If verified as authentic, the footage would provide the first public proof that Mr. Mengistu is alive after years of silence. The Israeli authorities were examining the video on Monday and did not immediately confirm its veracity.
Yallo Mengistu, a brother of the captive, told the Israeli news site Ynet that while he could not be 100 percent sure, the man in the video looked like Avera Mengistu.
There was no indication when the footage was taken, but the military wing of Hamas, which released the video on its Telegram account and website, accompanied the clip with text slides written in Arabic and Hebrew stating that the departing army chief, Aviv Kochavi, had “failed.” They also warned that his successor, Lt. Gen. Herzi Halevi, who was sworn in on Monday, “must prepare himself to bear the burden of that failure and its consequences.”
“Your predecessor left you with a lot of trouble and lies,” one of the slides said.
Appearing healthy, dressed in a blue shirt and looking straight into the camera, the man who identified himself as Mr. Mengistu in the video asked, in Hebrew, “How long will my friends and I remain in captivity here after long years of suffering and pain? Where are the state and the people of Israel?”
Mr. Mengistu, an Israeli citizen of Ethiopian descent, walked into the Palestinian coastal enclave of Gaza in September 2014, about two weeks after a cease-fire went into effect, ending a devastating 50-day war between Israel and Hamas. Mr. Mengistu, who was in his late 20s at the time, had walked along the beach to Gaza, according to security camera footage at the time. His hometown, Ashkelon, is about 10 miles to the north.
After a 10-month news blackout on the case, the Israeli authorities eventually confirmed that he was being held by Hamas along with another Israeli citizen, later identified as Hisham Al Sayed, from a Bedouin town in Israel’s southern Negev desert. Mr. Sayed had also crossed into Gaza independently. Last year, Hamas released a video clip of Mr. Sayed lying in a bed and breathing through an oxygen mask.
Mr. Mengistu’s family said that he had suffered from depression and was not drafted into the army at 18, like most Israeli Jews, but received an exemption after a medical committee found him unfit to serve.
Born in Ethiopia’s Gondar Province, Mr. Mengistu was airlifted to Israel with his family in 1991, at the age of 5.
Myra Noveck contributed reporting from Jerusalem.