The US will use its veto right if the UN Security Council passes a resolution on Palestinian statehood.
President Barack Obama mentioned the prospect when meeting with Palestinian President Mahmoud Abbas on the sidelines of the 66th session of the UN General Assembly in New York.
On Friday Mr. Abbas plans to submit to UN Secretary General Ban Ki-moon a formal request for UN membership for a new sovereign Palestinian state.
In case of a US veto the Palestinians may put the matter before the General Assembly where the majority of delegations are ready to vote yes.
Earlier French President Nicolas Sarkozy urged the UN to give the new Palestinian state an observer status with a roadmap to peace within a year.