The world's newest nation has struggled to draw a line under a five-year civil war that ended in 2018.
President Salva Kiir and his Vice President Riek Machar unable to agree on the implementation of the deal they signed.
The US has expressed "concern" over "growing tensions" in South Sudan, and called on all parties to respect a 2018 peace agreement after the opposition withdrew from a body overseeing the process.
The world's newest nation has struggled to draw a line under a five-year civil war that ended in 2018, with former rivals President Salva Kiir and his Vice President Riek Machar unable to agree on the implementation of the deal they signed.
Earlier this month, Machar's Sudan People's Liberation Movement in Opposition (SPLM/A-IO) announced its withdrawal from a body overseeing the peace process over "unprovoked" attacks on its bases by its "peace partner".
In a statement, US State Department spokesman Ned Price on Tuesday deplored "the recent clashes" in Upper Nile State and the SPLM/A-IO's withdrawal from the body, which "undermines the peace agreement."
"We call for both sides to observe fully their obligations under the existing peace agreement and note that inflammatory rhetoric is counterproductive and should cease immediately," he said.
Washington also calls on Kiir and Machar "to do their utmost to de-escalate tensions," he continued, adding that both sides "bear responsibility for the deteriorating situation."
Neither have "made good faith efforts to implement the provisions of the revitalized peace agreement," Price said.
Since achieving independence in 2011, South Sudan has spent almost half of its life as a nation at war.
Almost 400,000 people died in the civil war before Kiir and Machar signed a peace deal in 2018 and formed a unity government two years ago.
Since then, the country has lurched from crisis to crisis, battling flooding, hunger, violence and political bickering as the promises of the peace agreement have failed to materialize.