The United States says it is working with other nations to impose United Nations backed sanctions if the country does not sign and adhere to a peace treaty.
On Wednesday, President Barack Obama's national security adviser Susan Rice said in a statement that the U.S. was suggesting such sanctions "if an agreement is not signed by the government within 15 days and a ceasefire is not implemented promptly by all parties".
South Sudan President Salva Kiir refused to endorse a peace agreement suggested by regional leaders on Monday, saying he needed more time.
The war-torn country, which gained self-government from Sudan in 2011, degenerated into turmoil in December 2013 when a political dispute between Kiir and his second-in-command, Riek Machar, spiraled into violence that reopened tribal fault lines.
Seyoum Mesfin, the arbitrator for IGAD, the East African alliance leading the peace discussions, said Kiir's faction required a couple of weeks before endorsing the peace agreement that had been previously accepted by the South Sudanese insurgents.
According to Seyoum, "In the next 15 days, the government will come back to Addis Ababa to finalise the peace agreement." There was no immediate remark from the administration.
On Monday, the U.S State Department announced that it profoundly regretted the government resolution and advised it to sign within 15 days.
Many rounds of conciliation have failed to finish the armed conflict that has seen over 10,000 people lose their lives and displaced at least 2 million, with both parties engaging in a battle of attrition despite endorsing ceasefire agreements.
If South Sudan's administration will not endorse the peace agreement, "then we must all be firm on our next steps," Britain's UN assistant ambassador Peter Wilson said to the 15-member UN Security Council. "We cannot sit by while leaders fight and their people's suffering grow," he added.
Last month, IGAD settled on August 17th as the cut-off date to end the prolonged talks, outlining suggestions for ending the violence.
According to IGAD, the proposal entails a 30-month changeover period with Kiir as leader, with a first deputy president post given to the rebels.
In July, after at least one year of admonitions, the Security Council enforced its first sanctions on six army generals for accelerating the fighting.