US Secretary of State Condoleezza Rice has said that the proposed Palestinian government of national unity must accept Israel's right to exist.
Ms Rice reaffirmed Washington's support for Mahmoud Abbas
Ms Rice said the US was still examining the agreement between Hamas and the Palestinian President, Mahmoud Abbas.
The plan for a coalition was announced on Monday after months of talks.
Palestinians are hoping that a national unity government will open the way for international aid donors to end their boycott of the Palestinian authority.
The West imposed the ban after Hamas's surprise election victory in January.
But from Washington, where she held talks with Israeli Foreign Minister Tzipi Livni, Ms Rice said the unity government should first accept the principles outlined by the so-called Quartet, the grouping including the US, Russia, the EU and the UN.
"We do believe that the Quartet principles represent the consensus of the international community and the way forward between Israel and the Palestinians," she said.
The Quartet calls for a recognition of Israel's right to exist and for violence to be abandoned, among other measures.
Referring to Hamas's traditional hostility to Israel, Ms Rice added: "It goes without saying that it's hard to have a partner for peace if you don't accept the right of the other partner to exist."
On Tuesday, Israel cautiously welcomed plans for the unity government, but warned that any new leadership must meet conditions set by the West.