"Israel has expressed its readiness to extend the truce under its current terms," the official, quoted by the Reuters news agency, said, referring to the 72-hour deal brokered by Egypt that took effect on Tuesday.
But Hamas deputy leader Musa Mohammed Abu Marzouk, part of the Palestinian delegation holding talks in Cairo, denied on Wednesday night that there was yet any agreement for an extension.
"There is no agreement to extend the ceasefire," he wrote on Twitter.
"Any news about the extension of the truce is unfounded," added Hamas spokesman Sami Abu Zuhri.
This came as UN Secretary-General Ban Ki-moon said the deaths in Gaza "have shocked and shamed the world".
The UN chief has also called for investigation into bombing of UN facility in Gaza.
"Attacks against UN premises, along with other suspected breaches of international law, must be swiftly investigated," he added.
The Egyptian-mediated 72-hour ceasefire that went into effect on Tuesday has brought relief to both sides after fighting that erupted on July 8 killed 1,875 Palestinians and 67 people on the Israeli side.