Israeli authorities say two Israeli citizens are being held in the Gaza Strip, at least one of them by the Hamas.

The Israeli defence body responsible for Palestinian civilian affairs said Avraham Mangisto, an Israeli of Ethiopian descent, crossed the border fence into the Gaza Strip on September 7 last year, nearly two weeks after the end of the Israeli war on Gaza.

It was only on Thursday that a court lifted reporting restrictions on the case.

The name of the the other citizen, an Israeli Arab who Israeli newspaper Haaretz said had crossed the border with Gaza a number of times in the past, has not yet been released.

The Coordinator of Government Activities in the Territories (COGAT) said that "according to credible intelligence," Mangisto is being held "against his will" by Hamas.

Hamas said it did not know anything about it.

It is still unclear how and why Mangisto, a 28-year-old resident of Ashkelon, was captured. Some Israeli sources said he was swimming when a wave carried him closer to the Gaza Strip.

Al Jazeera’s Paul Brennan, reporting from West Jerusalem, said early reports suggested that Mangisto arrived to Zikim beach on the border on September 7, left behind his bag and crossed the border through a hole in the border fence. His motivation for doing so remains unclear.

Haaretz said that Mangisto was known to have suffered psychological problems in the past, and may have been drinking on the day of his disappearance.

COGAT said "Israel has appealed [to] international and regional interlocutors to demand his immediate release and verify his well-being".

The defence body said the second Israeli citizen being held in Gaza is an Arab citizen of Israel. It provided no further details.

Al Jazeera’s Walid al-Omari, reporting from East Jerusalem, said that the announcement would improve Hamas’ bargaining chip in a potential future release of prisoners held in Israeli jails.

As for the 10-month delay in announcing the disappearances, al-Omari said that Israel sees the abduction of both Israeli civilians and soldiers as a setback to its prestige.

"Such information is embarrassing to the Israeli government and Prime Minister Benjamin Netanyahu, especially in front of the Jewish minority of Ethiopian origin."

Source: Al Jazeera and agencies