Avera Mengistu
Israeli-Ethiopian Avera Mengitsu, 28, is believed to be held captive by HamasFacebook

Israeli prime minister Benjamin Netanyahu has said his government is working to return the two Israelis who crossed the border with the Gaza Strip, including one who is believed to be held captive by Palestinian militant group Hamas.

News of the disappearance of two Israelis broke out after an Israeli court lifted a long-standing gag order. Avera Mengistu, a 28-year-old Israeli-Ethiopian, apparently climbed over a fence into Gaza in September 2014. Hamas said the man, who has suffered mental health issues in the past, was detained, questioned and then released.

The second is an Israeli-Arab who crossed at Erez in April and is still being held by Hamas.

"We hold Hamas responsible for their welfare," Netanyahu said. "I spoke with the family of Avraham [Avera] Mengistu and told them that as soon as the incident was known we spared no effort to return them to Israel."

"I expect the international community, which expresses concern over the humanitarian situation in Gaza, to call for the return and release of our citizens," he said.

Haaretz newspaper, which challenged the gag order and first broke the story, said Mengistu's family had harshly criticised the Israeli government for its poor handling of the case. The family had not met Netanyahu and he had allegedly not responded to a letter sent after the incident.

Further to his psychological problems, Mengistu, who is from the coastal city of Ashkelon, had reportedly been drinking on the day he went missing.

Security cameras recorded him carrying a bag and approaching the Gaza fence. He had already climbed over when soldiers arrived to approach him. Mengistu left behind the bag which had a copy of the Hebrew Bible in it.

A Palestinian official said that Mengistu was released by Hamas after a short interrogation. According to the official, Mengistu left the Gaza Strip via a tunnel to Sinai, in an attempt to reach Ethiopia.

However, the coordinator of government activities in the territories said Mengisto is still being held "against his will" by Hamas. "Israel has appealed to international and regional interlocutors to demand his immediate release and verify his well-being," the coordinator told AP.

"This is a humanitarian matter and I expect those holding him to treat him properly and to return him in full health,"said Israeli President Reuven Rivlin in a statement.

A spokesman for Hamas, Salah Bardawil, declined to comment. "We don't have any information about it. Even if is true, we don't have instructions to talk about it," he said.

On Wednesday 8 July, Hamas leader Khaled Meshaal had told reporters in Doha that Israel had approached his party via a European mediator to negotiate the release of the bodies of soldiers Hadar Goldin and Oron Shaul, who went missing and were later declared dead during Operation Protective Edge.

He also alluded to Mengistu and the Israeli-Arab hostage, claiming that Hamas could not agree on any negotiations until Israel releases Palestinian prisoners from the 2014 war.

Mengistu's brother spoke to Haaretz voicing their family's frustration at the ordeal before Israel lifted the gag order.

"We are fed up. We want to go public with his story," Yalo told Haaretz. "The day it happened, a person from the Shin Bet security service or the police called me and said my brother was in Gaza. I told my parents and my siblings, and that's how we found out. But no one came to see us at our home."

"Two weeks after I contacted [an Israeli MP], the commander of the Gaza division came to see us for the first time," Yalo told the paper. "He told me they knew my brother was in Gaza, and that they have people who are keeping track of him and will bring him back – but that we should not tell people."

He said Israel's reaction would have been different had a white person walked into the Strip.

"It's more than racism – I call it 'anti-blackism,'" he said. "I am one million percent certain that if he were white, we would not have come to a situation like this."