Abu-Zuhri said "the atmosphere is not right for the signing of an accord".
Hamas, which governs Gaza, has asked Egypt to delay the signing of the deal, which Cairo as mediator had announced for later this month, a source within the group said on Wednesday.
Egypt had earlier announced that Hamas and Fatah of Palestinian President Mahmoud Abbas would travel to Cairo to sign the long-delayed reconciliation deal on October 25-26.
The postponement was requested because of the decision by the Palestinian Authority (PA) delegation at the UN Human Rights Council to drop its backing for an immediate vote on a report on the Gaza war, the Hamas source said.
The UN report, authored by Richard Goldstone, a South African judge, accused mainly Israel but also Hamas of committing war crimes during the 22-day war that killed 1,400 Palestinians and 13 Israelis last year.
Hamas has been at the forefront of criticism levelled at Abbas over the postponement of the Goldstone report vote, saying the move "betrayed" the Palestinian victims of the offensive.
Published at the end of September, the UN-sanctioned report identifies what it calls war crimes committed by Israel in Gaza between last December and January.
Such a vote would have been one of many steps to bring Israel before a war-crimes tribunal.
Abbas has since sought to backtrack, saying he welcomed a move by Libya to hold an emergency meeting of the UN Security Council to discuss the report.
The move by the PA came after it was strongly condemned for its delegate's perceived role in the vote's postponement.
Al Jazeera's Nour Odeh, reporting from the West Bank city of Ramallah, said the PA attempt to reconvene a UN meeting was "perhaps an admission that the outrage, public and official, across the Palestinian political spectrum, has been unbearable for the Palestinian president".
She said "this step is likely to defuse tensions, although it is still not clear whether the Palestinians will be able to secure enough votes from states to convene this session of the UN Human Rights Council".
Abbas's decision to support the deferral of the vote on the Goldstone report was linked to US pressure and Israeli threats to scuttle any hopes of peace talks.