Israel is seeking to extend the first stage of the ceasefire agreement in the war with Hamas in Gaza and is prepared to resume fighting if there is no progress in crucial talks this week, according to reports.

Israel’s Kan Radio, along with Ma’ariv, a daily newspaper, reported on Tuesday that informal talks were under way aimed at extending the first 42-day stage of the ceasefire, which expires on Saturday. Official internationally mediated negotiations on how to implement the second stage – which would involve a complete Israeli withdrawal from the Palestinian territory – were supposed to begin weeks ago, but have been repeatedly postponed as the fragile truce has lurched from crisis to crisis.

An extension of stage one would involve further hostage releases in exchange for Palestinian prisoners and detainees, but Israeli officials are sceptical of the idea’s workability.

The ceasefire is at an impasse before the scheduled release of four Israeli bodies on Thursday after Israel decided to postpone freeing 600 Palestinians last weekend. That decision appears to have been prompted by a film released by Hamas on Saturday in which two hostages were forced to watch the release of other captives. The video, together with handover ceremonies in which the hostages have been paraded around by the militant group, have infuriated public opinion in Israel.

Hamas has said it will not engage with any negotiations until the 600 Palestinians whose release was delayed are freed, putting mediators under pressure to resolve the latest dispute before the next release of hostage bodies on Thursday and the expiration of stage one two days later. The group had previously said it was open to a short extension of phase one in order to keep aid flowing to the territory and talks on stage two alive.

Egypt, a key mediator between the sides, has also refused to discuss an extension of the first phase unless phase two talks begin at the same time, AP reported on Tuesday, citing two officials.

Steve Witkoff, the Trump administration’s Middle East envoy, is returning to the region on Wednesday. In an interview with CNN over the weekend, he said he was aiming for an extension of stage one to ensure there would be time to negotiate stage two.

In stage two of the deal, of uncertain duration, Israel is supposed to completely withdraw its forces from Gaza, in effect ending the war, and talks on future governance of the strip should begin. Reconstruction is due to begin in stage three, but the sides remain far apart on Gaza’s future.

Hamas has said it is willing to give up control of the Gaza Strip to other Palestinians, but its leadership refuses to go into exile. Israel maintains that it will not allow Hamas or the West Bank-based Palestinian Authority to administer the territory when the war ends.

On Sunday, Israel’s prime minister, Benjamin Netanyahu, said Israel was prepared to return to hostilities in Gaza “at any moment” and vowed to complete the war’s objectives “whether through negotiation or by other means”.