A ceasefire to end a five-month conflict that has displaced 1.5 million people in South Sudan has come into effect.
President Salva Kiir and rebel leader Riek Machar signed the deal on Friday.
Troops would defend themselves if they came under attack, said the president's spokesman, but he added the government was not expecting any problems.
A previous deal, made in January, collapsed in days, with each side accusing the other of breaching terms.
The agreement was signed in the Ethiopian capital, Addis Ababa, after the rivals' first face-to-face meeting since hostilities began in December.
Earlier, the UN called on both sides to facilitate deliveries of emergency aid to a population in danger of mass hunger: The UN estimates that some five million of its citizens are in need.
Toby Lanzer, the UN's top aid official in the region, said roads and rivers must be opened for emergency relief.
South Sudan is the world's newest state, as well as one of its poorest.
As well as an immediate ceasefire, the deal envisages the creation of a transitional government ahead of the drafting of a new constitution and fresh elections.
But it is not clear how that government would be formed and, with many details of the deal yet to be worked out, officials caution that a lasting peace may still be some way off.
Mr Kiir's spokesman, Ateny Wek Ateny, told the BBC it was down to Mr Machar to rebuild the trust lost during the fighting that has cost thousands of lives.
"We hope that things will go well because the highest levels have signed the document and the other side, the rebels, they should also respect the words and signatures of their leaders," said the spokesman.
He denied the conflict had become a war on ethnic lines, between the Dinka tribe of the president and the Nuer tribe of his rival.
The UN has accused both the South Sudanese government and the rebels of crimes against humanity, including mass killings and gang-rape.
The violence began when President Kiir accused his sacked deputy Mr Machar of plotting a coup.
Mr Machar denied the allegation, but then marshalled a rebel army to fight the government.
The battle assumed ethnic overtones, with Mr Machar relying heavily on fighters from his Nuer ethnic group and Mr Kiir from his Dinka community.
The UN has about 8,500 peacekeepers in South Sudan. However, they have struggled to contain the conflict.
South Sudan gained independence in 2011, breaking away from Sudan after decades of conflict between rebels and the Khartoum government.