The oath had dropped a clause where ministers swear to be loyal "to the people and its national heritage", the lawyer said.
The United States congratulated the new Palestinian government on Sunday, a day after incoming Prime Minister Mohammad Shtayyeh announced his new cabinet alongside President Mahmud Abbas - leaving out Hamas.
"We were hoping and will hope to go for a national unity government that will be a salvation government that rescues the current national Palestinian status", said al-Hayya in a press statement.
Fatah and PLO President Mahmoud Abbas said talks with the U.S. are "useless", Arabs48 reported yesterday.
Mohammed Shtayyeh, an economist and longtime Abbas adviser, will serve as prime minister of the West Bank-based Palestinian Authority (PA).
"We have many hard missions, mainly the Deal of the Century, or the USA peace plan, which will be declared soon to resolve the Israeli-Palestinian conflict", the president affirmed.
Analysts say the change of government was made to further isolate Hamas, which has been at odds with the Fatah party of Abbas and Shtayyeh for more than a decade.
The new appointments "widen the Palestinian division at the expense of the Palestinian people's interests", it said, calling for a unity government that includes Hamas.
That year, Hamas won almost 45 percent of the vote during parliamentary elections, placing it in a position to lead.
"As you know, we've been trying with our Arab brothers since 2007 to reach reconciliation and solve the Gaza issue", he said, adding that Hamas took over Gaza Strip.