The United States may reassess its assistance to the Palestinians if militant Hamas group and moderate Fatah faction form a government together as a consequence of the surprise reconciliation agreement signed in Gaza.

The deal was criticised by Israel, which cancelled a negotiating session with representatives of the Palestinian Authority president Mahmoud Abbas. Hamas, which controls the Gaza Strip territory, refuses to recognise Israel's legitimacy and is blamed for allowing rocket attacks on Israel.

A US official told Reuters that any forthcoming Palestinian government "must unambiguously and explicitly commit to nonviolence, recognition of the state of Israel and acceptance of previous agreements and obligations between the parties".

"If a new Palestinian government is formed, we will assess it based on its adherence to the stipulations above, its policies and actions, and will determine any implications for our assistance based on US law," the official said.

Hamas is listed by the US and Israel as a terrorist organisation. A statement by Israeli prime minister Benjamin Netanyahu's office calls the radical Islamist group "a murderous terror organisation that calls for the destruction of Israel".

Washington was caught unaware by the Palestinian reconciliation agreement and called it a serious obstacle to nine-month-old peace talks brokered by secretary of state John Kerry.

"It's hard to see how Israel can be expected to negotiate with a government that does not believe in its right to exist," State Department spokeswoman Jen Psaki said.

Fatah broke ties with Hamas since factional fighting exploded after the militant group's victory in Gaza's Palestinian legislative council elections in 2006.

The two factions have announced similar accords previously, but were never implemented. As with the previous deals, the agreement gives Abbas five weeks to form a unity government.