"I'm not going to make pre-commitments in a negotiation on any particular topic," Vance said, though he maintained the proposal was "not currently" part of the plan.

The president said he may give leaders in Tehran until early next week to send another proposal to end the conflict diplomatically, or else the US may resume the war.

The US wants Iran to work with Washington on a process to ensure that the Iranians would not rebuild their nuclear weapons capacity in the years to come.