Sixty percent of American voters think US military action against Iran was "not worth it", according to a national poll from Quinnipac University.

Public sentiment appears to have shifted sharply after the signing of the Islamabad Memorandum of Understanding (MoU) with Iran, a pact to end hostilities for 60 days while the US and Iran negotiate terms for a permanent end to the war.

Voters, however, are split on the matter, with Democrats overwhelmingly feeling it wasn't worth it (93 percent) while 75 percent of Republicans felt the war was worth it. A majority of independents, 66 percent, felt the war was not worth it.

The scepticism extends to the diplomatic settlement itself, with the poll determining that 59 percent of American voters are either "not so confident" or "not confident at all" in the MoU.

Once again, Republicans had greater confidence in the deal, with 76 percent saying they were either "very" or "somewhat" confident the deal with Iran would work.