Miller told reporters Washington was working with the mediators on what the proposal will contain and ensuring that "it's a proposal that can get the parties to an ultimate agreement."
Talks over months have so far failed to reach a deal to end war, now in its twelfth month.
Palestinian resistance movement Hamas said last week it is ready to implement a ceasefire based on the previous proposal without any new conditions from any party.
Negotiations have been ongoing to clear two main obstacles: Israel's demand to keep its forces in the Philadelphi corridor to maintain a buffer between Gaza and Egypt, and the specifics of an exchange of hostages for Palestinian prisoners held by Israel.
Miller confirmed those remained the main sticking points.
AFP adds from Geneva: United Nations rights experts warned Monday that Israel risked becoming an international "pariah" over its "genocide" in Gaza, suggesting that the country's UN membership should be called into question.
Several independent UN experts decried what they said was Israel's escalating violence and rights violations in Gaza and the West Bank, its disregard for international court rulings and verbal attacks on the UN itself.
The rapporteurs, who are appointed by the UN Human Rights Council but who do not speak on behalf of the UN, also slammed Western countries' "double standards" and insisted Israel needed to face consequences for its actions.
"I think that it is unavoidable for Israel to become a pariah in the face of its continuous, relentless vilifying assault on the United Nations, (and) Palestinians," said Francesca Albanese, the UN's special rapporteur on the rights situation in the Occupied Palestinian Territory.
George Katrougalos, the UN special rapporteur on the promotion of democratic and equitable international order, demanded that Israel be held to the same standards as all countries, and condemned its repeated attacks on critical UN officials or agencies.
"We cannot anymore stand this kind of double standards and hypocrisy," he told reporters.
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