The US has warned South Sudan's president Salva Kiir and rebel leader Riek Machar not to violate the peace deal signed on Wednesday.
State Department spokesperson John Kirby said the US would "hold to account" those who breach the peace deal and would support sanctions against them, the BBC reported.
Mr Kirby said the US did not "recognise any separate reservations made about the agreement", made by President Kiir.
"To end the fighting we call on all parties to adhere to the permanent ceasefire within the next 72 hours and begin the process of implementing this agreement," he added.
The US had proposed a UN arms embargo and additional sanctions from 6 September unless the pact was signed by the 15-day deadline given to Mr Kiir last week, when it was signed by his rival.
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