South Sudan President Salva Kiir and his rival Riek Machar could face US sanctions for failing to form an interim government and fully implementing the peace agreement.
Secretary of State John Kerry said the US would never accept any excuse again by either side to the conflict in South Sudan.
A statement issued by the US Department of Foreign Affairs, explained that Washington, as one of the greatest friends of South Sudan, had been instrumental in its political affairs and had injected billions of dollars to finance infrastructural development before and after the country attained its independence four years ago.
South Sudan activist and analyst Edmund Yakani welcomed the US plans to hold the two principals individually accountable for unwillingness to commit themselves to implement the peace deal.
"Yes, it is a good move to press the two to implement the peace agreement they assigned recently," he said. Mr Yakani said the choice of the people of the country was peace and stability.
The US warning comes at a critical time, after President Kiir recently appointed Dr Machar as the first vice-president, but the two have delayed forming the Government of National Unity since the latter gave conditions for his return to Juba.
Dr Machar insists on the demilitarisation of the capital as per the peace deal. Earlier, the US lobbied the UN Security Council to impose an arms embargo on South Sudan should the parties to the conflict fail to honour the peace deal, but China and Russia opposed the proposal.
The African Union also threatened to sanction the two leaders should they continue violating the peace agreement. President Kiir announced on Tuesday he would form the interim administration on the first week of March.