Al-Ahmad, who is also the head of Fatah delegation for the Cairo talks, said what was agreed upon two weeks ago under the auspices of Egypt is empowering the legitimate government to operate in accordance with its powers in accordance with the Basic Law in effect in the West Bank.
According to the agreement, the Western-backed Palestinian Authority will resume all governing responsibilities in Gaza no later than December 1.
Abbas welcomed the deal in comments to AFP and said he considered it a "final agreement to end the division" - though many details remain to be resolved and previous reconciliation attempts have repeatedly failed.
The Secretary-General also reiterated that the United Nations stands ready to continue working with Palestinian authorities and the region to support the Government in assuming its responsibilities in Gaza.
"Hamas will spare no effort to turn this agreement into a reality with a view to confronting the Zionist project and establishing a sovereign state of Palestine", al-Arouri asserted.
Last week, Palestinian Authority prime minister Rami Hamdallah visited Gaza for the first time since 2015 and his ministers took formal control of government departments in the territory. And he said a reconciliation deal makes peace harder to achieve.
However in September Hamas agreed that it would give up its power over Gaza, paving the way for this week's reconciliation talks.
Al-Ahmed told reporters after the ceremony that there has been "full agreement" to empower a national unity government to assume its full authorities in Gaza.
The same source, who preferred anonymity due to restrictions on speaking to media, said Hamas and Fatah had also agreed to allow the unity government to assume full responsibility for all of Gaza's border crossings by November 1.
He added that sanctions taken by Abbas against Gaza will also soon be lifted.
Ismail Haniyeh said in a statement that details would be announced in Cairo later on Thursday.
Egypt, which hosted a series of meetings between both parties over the past two days, invited Palestinian factions who signed the 2011 Accord to hold their coming meeting on November 21, 2017, said the statement.
Faced with increasing isolation and a severe electricity shortage, Hamas has reached out to Cairo for help, hoping to have the Rafah border with Egypt opened.
Cairo is now leading efforts to heal a decade-long political split between Gaza-based Hamas and the West Bank-based Fatah movement of Palestinian President Mahmoud Abbas.
The move should ensure a unity government will once again administer both the West Bank and Gaza after the rift caused by militant group Hamas' takeover of the Gaza Strip in 2007.