The release of hostages under a temporary truce between Israel and Palestinian Hamas militants will not happen before Friday, Israel’s national security adviser said, thwarting hopes of relatives that some would be freed on Thursday.

Israel and Hamas had agreed early on Wednesday to a ceasefire in Gaza for at least four days, to let in humanitarian aid and free at least 50 hostages held by militants in the enclave in exchange for at least 150 Palestinians jailed in Israel.

Israeli officials said earlier Wednesday that the deal would begin to be implemented on Thursday, but Hanegbi said later that the “negotiations on the release of the hostages continue all the time” and the “beginning of their release will take place according to the original agreement and not before Friday.”