UN Secretary General Antonio Guterres on Saturday said it was "unacceptable" South Sudan's warring parties had yet to make peace as a deadline approaches for the rivals to join forces in government.
President Salva Kiir and rebel leader Riek Machar have failed to break a deadlock over key terms of a power-sharing agreement with just two weeks until they are to form a unity government.
The pair have already missed two previous deadlines to settle their differences and enshrine a lasting peace to put an end to six years of bloody civil war that has left 380,000 people dead and millions more in dire poverty.
"Think about your people, respect your people, you have not the right to continue the confrontation when your people are suffering so much," Guterres told reporters in Addis Ababa ahead of an African Union summit.
"It is your moral and political responsibility to put an end to this and to find the agreements that are necessary to make South Sudan enter into a normal life."
Kiir and Machar signed a peace deal in September 2018, pausing the bloodshed that erupted in 2013 when the president accused his former deputy of plotting a coup.
They agreed to come together in a coalition in May the following year, however disputes over territory and security arrangements dogged negotiations and the deadline was missed, followed by another six months later.
In November, the pair were given 100 more days to resolve these sticking points as fears grew that the tenuous ceasefire could be derailed if a breakthrough was not achieved.
But progress has been piecemeal as the new February 22 looms nearer.
"It is for me totally unacceptable that we are again closing to a deadline ... and there is no agreement on a number of issues," Guterres said.
"It is time for the South Sudanese leaders to agree to cooperate, and to deserve the wonderful people they have."
A UN rights commission on South Sudan warned Friday that violence was on the rise in parts of the country, and that efforts to unify armed factions under the terms of the peace agreement were faltering.