"This is one of many ideas," a White House spokesman told AFP, but he stressed that President Donald Trump has not signed anything.
Iran says it rejects a ceasefire in response to "an American" proposal but stresses "the need for a permanent end to the war while respecting Iran's views," the state news agency Irna reports.
Mediators from Pakistan, Egypt and Turkey have been involved in negotiations on the new proposal, sources told Reuters and the news site Axios.
It is reported to contain two phases: a time-limited ceasefire followed by a more detailed peace agreement.
Donald Trump has threatened to escalate attacks on Iran if the country does not open the Strait of Hormuz by Tuesday evening.
