South Sudanese President Salva Kiir has ordered all government troops to cease fighting rebel forces as part of a peace agreement, his spokesman said, ahead of a full ceasefire on Saturday.

South Sudanese President Salva Kiir has ordered all government troops to cease fighting rebel forces as part of a peace agreement, his spokesman said, ahead of a full ceasefire on Saturday.

Kiir has ordered all the army "to stop shooting and remain in their barracks where they are, but they can shoot in self defense once attacked," spokesman Ateny Wek Ateny told AFP on Friday.

Both sides accused each other of launching attacks on Wednesday as Kiir signed a peace deal aimed at ending the 20-month long civil war in which tens of thousands of people have been slaughtered.

The accord, already signed by rebel chief Riek Machar, gave a 72-hour deadline for a permanent ceasefire, which comes into effect around sunset on Saturday.

Late on Thursday, rebels accused the army of attacking their positions in the northern battleground state of Unity. The army did not respond, but has previously dismissed rebel claims as lies, or accused them of launching attacks.

Facing the threat of international sanctions, Kiir signed the deal but annexed a list of reservations that he said would have to be addressed for the deal to take hold in the world's newest nation.