After applauding the Palestinians' efforts, Greenblatt drew attention to Washington's demands from the new united Palestinian government: "The United States reiterates the importance of adherence to the Quartet principles: any Palestinian government must unambiguously and explicitly commit to nonviolence, recognize the State of Israel, accept previous agreements and obligations between the parties - including to disarm terrorists - and commit to peaceful negotiations".
Earlier Thursday, Greenblatt had called on Hamas to abandon its policy of armed resistance to Israel - and officially recognize the self-proclaimed Jewish state - within the context of a sought-for Palestinian unity government.
Hamas and Fatah, two rival Palestinian factions, recently reached a reconciliation agreement in Cairo and will begin negotiations to form a unity government in November.
On Wednesday, Israel's security cabinet said it would not enter talks with any Palestinian unity government until Hamas met a long list of demands.
"I think we should clarify our position to the Americans that the unity deal will help the political process and will help bring peace", Fatah's Qawasmeh said. "We declare that our decision is a Palestinian, independent, national decision and we will not go back to division", he added.
"These groups, which initially received support from the U.S. and its allies, eventually turned into monsters threatening their supporters and creators", Press TV quoted him as saying.
The fresh Hamas-Fatah reconciliation efforts have enraged Israeli Prime Minister Benjamin Netanyahu, who said that the regime would not accept "imaginary appeasement where the Palestinian side is reconciling at the expense of our existence".
Prime Minister Benjamin Netanyahu commended the USA on Thursday for making clear that Hamas must disarm, recognize Israel and accept previous agreements.
Last week, Hamas leaders and Palestinian President Mahmoud Abbas' Fatah party signed an Egyptian-brokered reconciliation agreement, where Hamas agreed to hand over ruling of the Gaza Strip to Abbas' consensus government.
The two groups have governed the occupied Palestinian territories of the West Bank and the Gaza Strip respectively ever since.
Additionally, Hamas spokesman Hazem Qassem said that "the conditions [set] by the occupation reveal that Israel is greatly injured by the reconciliation", adding however that such an attitude is nothing new.