Juba, South Sudan (CNN) -- East African leaders on Friday gave South Sudan's warring factions four days to lay down their arms after nearly two weeks of widening violence.
If they don't, the leaders of the Intergovernmental Authority on Development (IGAD) warned they'll "take action" to stop the conflict that the United Nations says has killed more than 1,000 and forced some 121,000 from their homes.
The warning came the same day the United Nations said the first of 5,500 additional peacekeepers had arrived in the country.
The leaders of the IGAD didn't specify what sort of action would be taken. But a communique issued Friday in Nairobi, Kenya, appears to throw the group's weight behind South Sudanese President Salva Kiir.
In a joint statement by the leaders of the IGAD said they would not accept a violent overthrow of the country's democratically elected government, and said any change must come through the democratic process.
Kiir has accused rival politician Riek Machar, his former vice president, of trying to stage a coup. Machar has denied involvement in a coup.
Fighting broke out between Kiir's government and supporters of Machar on December 15 in the capital city of Juba. It quickly spread across the country, with reports of mass killings as evidenced by mass graves.
Kiir and Machar are longtime rivals from two different tribal clans -- Kiir is from the Dinka tribe, Machar from the Neur.
South Sudan's government said it has agreed "in principle" to a cease-fire demanded by the IGAD, Information Minister Michael Makuei Lueth told CNN.
Leith said Kiir's government is open to "unconditional dialogue" to end the violence.
The Intergovernmental Authority on Development appointed envoys from Kenya and Ethiopia to help broker a deal.
Machar hasn't responded to the proposal, leaving it unclear Friday what immediate impact the agreement would have on the fighting.
The news of a possible deal comes as United Nations officials work feverishly to finalize details of sending peacekeeping reinforcements to South Sudan. The U.N. hopes to send them in no later than Saturday to help protect the 50,000 people now crowding U.N. bases, seeking shelter from the fighting.
On Friday, 72 peacekeepers arrived in Juba, according to the United Nations. It was the first group of an additional 5,500 peacekeepers approved by U.N. Security Council. The additional personnel will increase the total peacekeeping force in South Sudan to 12,500 soldiers and 1,323 police officers.
Meanwhile, U.N. officials and aid workers struggled to protect and provide food, shelter and medical care to those who have fled the fighting, which has spread to seven of South Sudan's 10 states, according to the United Nations.
More than 63,000 people have crowded on to U.N. bases in South Sudan seeking shelter from the violence, requiring a massive influx of aid.
U.N. workers on Friday were able to resupply a U.N.-operated hospital in Malakal, U.N. Assistant Secretary-General Toby Lanzer said on Twitter.
The U.N. Humanitarian Air Service also began flying in aid workers and supplies, he said.
CNN's Azadeh Ansari, Nana Karikari-apau, Moni Basu, Chelsea J. Carter in Atlanta, and journalist Kenneth Mijungu in Nairobi, Kenya, contributed to this report.