Israel is holding the bodies of two Palestinians killed near border with the Gaza Strip, an Israeli official confirmed on Sunday.

Maj. Gen. Yoav Mordechai, the outgoing Coordinator of Government Activities in the Territories, said Israel will not return the bodies of the two Palestinians until two Israelis held by Palestinian group Hamas are returned, Anadolu Agnecy reports.

“Israel will not rest and the residents of Gaza will not know peace until the Israelis are returned from the Gaza Strip and our soldiers will be brought for burial in Israel,” he said in a Facebook post in Arabic.

READ: Rights groups slam court delay in ruling on Israel’s withholding of Palestinian bodies

Hamas, which rules the Gaza Strip, is believed to be holding four Israelis since 2014, but refuses to specify whether they were dead or alive.

With the two bodies, the death toll of Palestinians killed by Israeli gunfire during rallies demanding the return of refugees near the Gaza border rises to 17.

Israel is already holding the bodies of 24 Palestinians since 2014, when the Israeli army launched a deadly offensive on the blockaded territory.

On Saturday, the Israeli army threatened a “stronger response” to Palestinian protests along border with the Gaza Strip.

Friday’s rallies were the start of a six-week protest that culminates on May 15, the day the Palestinians call as “Nakba”, or “Catastrophe”, when Israel was created.

The demonstrators are demanding that Palestinian refugees be allowed the right of return to towns and villages which their families fled from, or were driven out of, when the state of Israel was created in 1948.