The White House on Wednesday welcomed the decision by South Sudan President Salva Kiir to belatedly sign a peace accord, but warned his endorsement should not come with caveats.

"President Kiir made the right decision to sign the peace agreement," said spokesman Josh Earnest, adding "the US does not recognize any reservations or addendums to that document."

Facing international sanctions, Kiir earlier signed the deal, designed to end 20 months of brutal internecine fighting, but repeatedly expressed reservations.