Hamas said it would postpone this week’s release of Israeli hostages due to disputes over security and humanitarian goods, the most serious challenge yet to a fragile cease-fire under which another 17 Israeli hostages or their bodies are to be returned to Israel over the coming weeks.

Hamas has threatened to stall the next release of hostages from the Gaza Strip to Israel, accusing the Jewish nation of violating the terms of the ceasefire deal, which was previously agreed upon in January.

Israel completed its withdrawal from the Netzarim Corridor on Sunday, a key road that splits Gaza in half, as part of its commitments under a ceasefire agreement with Hamas.