Reconciliation could also pose a dilemma for worldwide efforts to reach an Israeli-Palestinian peace deal since Hamas has not recognized Israel, unlike the Abbas-led Palestine Liberation Organization.
With Hamas in control, conditions in Gaza deteriorated.
While Israeli Prime Minister Benjamin Netanyahu said that he is waiting for developments following the signed reconciliation deal between the Palestinian Authority (PA) and Hamas, not everyone in the Israeli government is satisfied with this answer including Israeli Education Minister Naftali Bennett.
In an online posting later, Netanyahu warned that the deal would make "peace much harder to achieve".
"Israel should end its siege on Palestinian lands and avoid any movement that would harm the reconciliation process", he said. "Say yes to peace and no to joining hands with Hamas", he said.
Hamas, Fatah pen landmark reconciliation deal in Cairo
The Fatah official stressed that President Mahmoud Abbas instructed the delegation not to return without a reconciliation deal. Hamas seized Gaza from Fatah in a near civil war in 2007 and the two factions have been at loggerheads ever since.
But, after the reconciliation deal thousands of Palestinians now look forward to better times ahead. From now, any Israeli cooperation with Abbas is cooperation with Hamas.
Arouri is believed by Israel to have planned numerous terrorist attacks including a kidnapping-murder of three Israeli teens in the West Bank, considered among the main catalysts of the 2014 Israel-Hamas war.
The Palestinians said they were establishing committees to iron out details about security, elections, salaries and other administrative details in this latest try at unity government, but there was little or no mention of Israel at their press conference in Cairo on Thursday.
There has been a period of relative calm between Israel and Hamas in the Gaza Strip since 2014's confrontation between the two, with the militant group instead focused on carrying out acts of violence in the West Bank and Israel.
All previous Fatah-Hamas attempts to reconcile have quickly broken down.
Under the terms of the deal, the Ramallah-based Palestinian unity government will assume political and administrative responsibility for the Gaza Strip no later than December 1. A year of tense unity government administration ended after fights in 2007 which led to Hamas expelling Fatah from the coastal enclave altogether.