The US says it shares concerns that Tunisia’s new constitution could weaken democracy and erode respect for human rights and fundamental freedoms.
It comes after the approval of a new Tunisian constitution that gives sweeping powers to the president in the 25 July referendum marked by low voter participation.
The referendum, which delivered a yes vote of 94.6% with a turnout of 30.5% - was boycotted by opposition parties.
The US State Department has urged an inclusive and transparent process in the future that would involve Tunisians who did not participate or opposed the referendum.