FACTBOX: U.S. responses to Israel's Gaza attacks

(Reuters) - Israel's attacks on Gaza three weeks before Barack Obama becomes U.S. president pose an unexpected challenge for a man who has promised to work for Middle East peace from his first day in office.

Questions have emerged over the timing of the attacks during a period of transition in the United States and over how Obama might respond as president and Hillary Clinton as his secretary of state.

Such questions often arise because Washington traditionally plays the role of broker in any Middle East peace moves.

HOW HAS THE UNITED STATES RESPONDED?

The Bush administration, due to hand over to Obama on January 20, put the onus on Hamas, the Islamists in charge of Gaza, to prevent more violence. It did not demand an end to Israeli attacks but urged all concerned to protect innocent lives.

Steven Cook, senior fellow for Middle East studies at the Council on Foreign Relations, said: "There's little that the United States can do to call the Israelis off. The Bush administration and the incoming administration are going to be hard pressed to find something productive that they can do immediately."

WHAT DID THE UNITED NATIONS SAY?

The strikes against Hamas have killed hundreds of Palestinians, prompting a U.N. Security Council call for a ceasefire. But an Israeli official said Israel was feeling little international pressure to halt its attacks.

WHAT HAS OBAMA SAID?