Mohammad Mustafa's appointment comes after mounting pressure to overhaul the governing body of the occupied Palestinian territories and improve governance in the occupied West Bank where it is based.

Hamas said the decision was taken without consulting it despite recently taking part in a meeting in Moscow also attended by Abbas' Fatah movement to end long-time divisions weakening Palestinian political aspirations.

"We express our rejection of continuing this approach that has inflicted and continues to inflict harm on our people and our national cause," Hamas said in a statement.

"Making individual decisions and engaging in superficial and empty steps such as forming a new government without national consensus only reinforces a policy of unilateralism and deepens division."

At a time of war with Israel, Palestinians needed a unified leadership preparing for free democratic elections involving all components of their society, it added.

In the West Bank, Fatah fired back at Hamas' criticism of Abbas, blaming it for what had befallen Gaza since it unilaterally carried out "the Oct7 adventure."

"Has Hamas consulted the Palestinian leadership as it is negotiating with Israel now and offering the concessions, in a bid to secure guarantees of its leaders' personal safety in return?" said the Fatah statement.

FOREIGN DEMANDS

As president, Abbas remains by far the most powerful figure in the Palestinian Authority, but the appointment of a new government showed willingness to meet international demands for change in the administration.

Mustafa, who helped organise the reconstruction of Gaza following a previous conflict, was assigned to lead the relief and rebuilding of the area, which has been shattered by more than five months of war, and reform Palestinian Authority institutions, according to the designation letter.

He replaces former Prime Minister Mohammed Shtayyeh who, along with his government, resigned in February.

Arab and international efforts have so far failed to reconcile Hamas and Fatah, which makes up the backbone of the PA, since the Hamas 2007 take over of Gaza, a move that reduced Abbas's authority to the Israeli-occupied West Bank.

Palestinians want both territories as the core of a future independent state.

Hamas said any attempt to exclude it from the political scene after the war was "delusional."

In a recent warning, a security official told a Hamas-linked news website that attempts by clans or community leaders to cooperate with Israel's plans to administer Gaza would be seen as "treason" and met with an "iron fist."

But the group denied media reports it killed some local clan leaders in recent days for meddling with aid distribution.