Al Jazeera's Amr El-Kahky, reporting from Cairo, said the apparent breakthrough came after senior Hamas officials met Omar Suleiman, the Egyptian intelligence chief, on Thursday.
Egyptian officials have been mediating between Israel and Hamas for weeks.
Taher al-Nono, a member of the Hamas delegation in Cairo, said "most of the obstacles that prevented us from reaching an agreement were resolved".
But Khalil Jahshan, a Middle East consultant and lecturer in international studies at Pepperdine University in the US, cautioned that "we've been here before, ad nauseam".
He told Al Jazeera that neither Hamas nor Israel would be interested in revealing the sequence or substance of their agreement because "it would defy, basically, the logic of the fighting of the past couple of months".
"This type of agreement could have been reached without the killing and savagery that we have witnessed during the Gaza war," he said.
Details of the deal could also be "very embarrassing" because Israel would have to admit that it was not just indirectly talking to Hamas but making a deal with a group it deems to be a "terrorist organisation" – things it said it would never do.
Israel had also said it would never open the crossings with Gaza before the release of Gilad Shalit, the Israeli soldier captured by Palestinian fighters in a cross-border raid in June 2006, but it appeared it was going to do so before his release, Jahshan said.
Abu Marzouq said the agreement was not linked to any possible prisoner exchange deal with Israel that would see the release of Shalit.
"This is a separate issue that has no relation with the truce," he said. "Gilad Shalit will be [released] in exchange for Palestinian captives."
Hamas has previously demanded that Israel free 1,400 Palestinian prisoners in exchange for Shalit.
Jahshan said that Hamas would not want it revealed that there will be some conditions placed on the crossings with Israel and the Rafah crossing with Egypt.
The longer-term truce deal would take the place of fragile ceasefires declared separately by Israel and Hamas last month which ended Israel's 22-day military offensive on the Gaza Strip.
About 1,300 Palestinians, at least a third of them women and children, were killed during the war. Fourteen Israelis died.
Gaza war inquiry
The UN secretary-general's office announced on Thursday that an inquiry had been opened into incidents in Gaza during the war.
|About 1,300 Palestinians were killed in Israel's 22-day offensive on Gaza [AFP]
Comprising members from Britain, the US, Sri Lanka and Switzerland, the board is to "review and investigate a number of specific incidents that occurred in the Gaza Strip" in which death or injuries occurred at UN premises or damage was done to UN premises or operations.
Hamas sources told Al Jazeera that once the ceasefire was in place all crossing points into the Palestinian territory would be opened.
The group said it would accept Israel continuing to ban the import of so-called "dual-use" items which could be used for military purposes, such as some construction material, provided that alternatives could be found.
Hamas has repeatedly sought guarantees that Israel will lift the blockade it has enforced on Gaza since Hamas seized the territory from forces loyal to Mahmoud Abbas, the Western-backed Palestinian president, in June 2007.
Abu Marzouq said Egypt was the main guarantor of the deal.
Egypt, a regional mediator and the only Arab state other than Jordan to have signed a peace deal with Israel, said earlier that it would announce "positive" results from the talks in the coming hours.
A deal would help restore Cairo's regional image after it was criticised in the Arab world for not opening its Rafah border crossing with Gaza and for its limited humanitarian operation during Israel's offensive.