Israel has said it is ready to extend the calm "indefinitely" but Hamas has so far hedged its bets, with an official on the negotiating team saying a decision would be taken later.
But as nightfall loomed, a senior Palestinian official accused Israel of procrastinating, warning it could lead to as resumption of the fighting when the deadline expires at 0500 GMT on Friday.
"The Israeli delegation is proposing extending the ceasefire while refusing a number of the Palestinian demands," he said, without elaborating.
"If Israel continues its procrastination, we will not extend the ceasefire."
In Gaza, local residents resigned themselves that the truce could be in jeopardy. Many are still sheltering in schools, reluctant to return to their damaged homes without a lasting truce.
"Everything is possible, everything is ready, if there are no demands (met at the talks), there will be more destruction," said Najib Habib, 35, a labourer from Shejayah, one of the worst-hit areas.
Four weeks of bloodshed between Israel and Hamas killed 1,886 Palestinians, and 67 people on the Israeli side, almost all soldiers.
Figures released by UNICEF, the UN children's fund, indicate that 73 percent of the Palestinian victims -- or 1,354 people -- were civilians. Of that number, at least 429 were children.
Hamas and Palestine Liberation Organisation (PLO) officials have laid out a number of demands, starting with the lifting of Israel's eight-year blockade on Gaza.
They also want the crossings with Egypt and Israel reopened and the release of around 125 key prisoners held in Israeli jails.
Israel's negotiating team, which had earlier flown back for consultations with Prime Minister Benjamin Netanyahu and Defence Minister Moshe Yaalon, was returning to Cairo, an Israeli official told AFP, without saying what was discussed.
"We haven't been formally notified of Israel's response regarding the Palestinian demands but we have learned informally... that it wants to procrastinate and stall in the negotiations to avoid (giving us) the achievements of the ceasefire," another Palestinian official told AFP in Cairo.
In Gaza, Hamas spokesperson Fawzi Barhum said there was no official stance on either renewing the truce or resuming the fighting, but an anonymous official familiar with the talks was pessimistic.
"The factions currently think they will resume fighting tomorrow morning," he told AFP.
Uncertainty all round
"Right now there is uncertainty, on the one hand the public in Gaza and in the region and the international community is telling (Hamas) not to ... leave negotiations," a senior Israeli military official said.
"On the other, the military wing of Hamas is warning they could restart the rocket launches."
Despite the withdrawal of all its troops from Gaza by the time the three-day truce began early on Tuesday, Israel has retained forces along the border who are ready to respond to any resumption of fighting.
Speaking in Jerusalem after a visit to Gaza, International Committee of the Red Cross president Peter Maurer said he was "deeply distressed and shocked" at the impact of violence, saying the scale of the civilian losses must not happen again.
And he suggested there may have been some violations of international humanitarian law which had not been "accurately and ambitiously implemented."
"The Geneva Conventions have been designed to protect and assist people, and I cannot be satisfied... when after four weeks of armed conflict we see the amount of destruction and the amount of victims."
With the guns silent, some semblance of normal life has returned to Gaza with traffic clogging the streets and people bustling about their business as shops, banks and markets resume business.
In some areas, there are scenes of utter devastation, with certain districts reduced to an endless sea of rubble and shattered hulks of buildings, an AFP correspondent said.
US President Barack Obama upped the pressure on the talks by saying Gaza could not remain forever cut off by Israel's blockade which has been in place since 2006.
"Long-term, there has to be a recognition that Gaza cannot sustain itself permanently closed off from the world," he told a news conference in Washington, saying the Palestinians needed to see "some prospects for an opening of Gaza so that they do not feel walled off."
And London, Paris and Berlin tabled an initiative offering an outline for rebuilding Gaza while ensuring Israel's security concerns were properly addressed, a diplomatic source said.
The proposal aims to strengthen the hand of Palestinian president Mahmud Abbas and his Palestinian Authority while clamping down on Gaza-based militant groups.
It also envisages opening the Rafah border crossing with Egypt then eventually opening other crossings to Israel. It also refers to the opening of a commercial port in Gaza, the source said.