Avraham Mengistu, 28, an Israeli citizen, crossed into the Hamas-controlled Gaza Strip on September 7, 2014. He has since been kidnapped by the Palestinian terror group, and they have refused to let him return home, Israeli officials said Thursday.

“According to credible intelligence, Mengistu is being held against his will by Hamas in Gaza,” said a statement from Israeli authorities. The statement also alleged that an unnamed Arab citizen of Israel had been abducted by Hamas.

Israeli Prime Minister Benjamin Netanyahu said Thursday that he holds Hamas responsible for the abductions and expects the terror group to release Mengistu and the unnamed Israeli back into Israel.

“We are working for the return of two Israelis who crossed the border into Gaza,” said the Israeli Prime Minister. “We see Hamas as responsible for their safety.”

“Yesterday I spoke to the parents and the brother of Avraham Mengistu. I told them that from the moment that the incident was known, we were not sparing any efforts to return him home,” Netanyahu added.

Israeli President Reuven Rivlin told the media that he is also working to free Mengistu. A statement from Rivlin read:

This is a Humanitarian issue, and we expect those holding him to behave accordingly and return him in good health. According to information which has arisen, Mengistu is being held by Hamas in the Gaza Strip. We will continue to make every effort in order to bring an end to this incident, as soon as possible.

NBC News reports that Hamas has refused several of its requests for comment on the issue.

Mengistu’s brother told reporters on Thursday that his brother is “not healthy” from a mental standpoint and called upon “the international community to engage and use their power to free my brother.”

Mengistu’s father, Ayelin, told an Israeli television news channel that his son suffers from depression and “used to go missing” for days at a time.