Washington - The United States is pushing for a ceasefire in the Gaza Strip that would require Hamas to halt rocket attacks into Israel but would also open crossings into the isolated enclave, US State Department spokesman Sean McCormack said Monday.

Secretary of State Condoleezza Rice spoke to more than a dozen counterparts over the weekend seeking support for the proposal, which would also address tunnels used by Hamas to smuggle weapons from Egypt, McCormack said.

The goal is to create a "sustainable, durable ceasefire" that would bring a lasting end to Hamas rocket attacks into southern Israel, which triggered Israel's military offensive in Gaza nine days ago.

More than 500 Palestinians have died in the fighting. Israel has rejected international calls for an immediate ceasefire, seeking to cripple the Hamas radical movement enough to keep it from firing rockets into Israel.

President George W Bush said Monday that any ceasefire would have to ensure Hamas cannot continue rocket attacks.

"All of us, of course, would like to see ... violence stop, but not at the expense of an agreement that does not prevent the crisis from happening again," Bush said.

Rice spoke with foreign ministers in the Middle East, including Israeli Foreign Minister Tzipi Livni, as well as with her counterparts in Europe. Among them were British Foreign Secretary David Miliband, and the French and German foreign ministers Bernard Kouchner and Frank Walter-Steinmeier.

Rice cancelled a trip to China to handle the crisis in the Middle East. Israel launched its massive air assault on December 27, and began a ground invasion on Saturday.

McCormack again urged Israel to take steps to avoid civilian casualties.

"Every sovereign state needs to decide for itself how best to defend itself," McCormack said. (dpa)