Israeli and Palestinian negotiators agreed to extend a temporary ceasefire in Gaza by 24 hours on Monday night, as talks in Cairo struggled to secure a long-term deal to end the six-week conflict.

Long negotiations ended late on Monday night with the Palestinian delegation claiming the two sides were still some way from an agreement, and hinting that the ceasefire would not be extended again if a lasting truce still could not be finalised on Tuesday.

"Until now there is no progress," said Azzam al-Ahmad, the chief Palestinian negotiator, as the previous five-day ceasefire ended at midnight. "There are hidden voices who are trying to put obstacles in our way. We have agreed on an extension for another day – just one day. Whether we agree or not, just one day."

Negotiators spent Sunday and Monday conducting indirect talks mediated by Egyptian intelligence officers, but failed to reach agreement about a draft treaty proposed by Egyptian officials on Sunday.

According to leaks, the outline agreement included the opening of crossings between Israel and Gaza, the import of construction materials under international supervision, and the expansion of the permitted fishing zone to 12 miles over a period of six months.

The demand for a seaport was reportedly agreed in principle, but detailed discussions have been deferred for at least a month. There was no mention of a parallel Palestinian demand to rebuild and reopen an international airport in Gaza.

A Palestinian demand for the release of dozens of Hamas members arrested by Israel over the past few months was also deferred.

Israel wants the disarmament of Hamas and other militant groups in Gaza as well as the return of the remains of two soldiers killed in fighting which Hamas is believed to be holding. All Palestinian factions say the demilitarisation of Gaza is not up for negotiation. But Hamas publicly claims it is ready to share power in Gaza with the Palestinian Authority, which currently runs the West Bank.

The war in Gaza, which began on 8 July, is the most intense of three conflicts in the past five and a half years, with massive destruction of homes, mosques, schools and hospitals, and the shelling of six UN premises being used to shelter people who had fled the fighting.

The Palestinian death toll on Monday stood at 2,016, including 541 children. More than 10,000 people have been injured and around 17,000 homes destroyed or severely damaged.

Israel has lost 64 soldiers in fighting, including five killed by friendly fire. Three civilians – two Israelis and a Thai agriculture worker – were killed by rockets launched from Gaza.

Robert Serry, the UN's most senior official for the Middle East, told the security council on Monday that "the volume of reconstruction will be about three times" what it was after the 2008-9 Gaza conflict. The scale of destruction and corresponding humanitarian needs were unprecedented, he said.

"Reconstruction of the magnitude which is now needed can only be addressed with the involvement at scale of the Palestinian Authority and the private sector in Gaza, meaning larger quantities of materials are required to enter Gaza."

On Monday, Egypt promised to host a donors' conference in Cairo to help raise money for Gaza's reconstruction, once a lasting ceasefire is eventually brokered.