The appointment of the first Muslim prime minister in the Central African Republic (CAR) has been rejected by the mainly Muslim rebel group Seleka.
Mahamat Kamoun was appointed in the wake of a deal signed last month between rival militias aimed at ending more than a year of religious conflict.
He is the first Muslim prime minister in the Christian-dominated country and is to lead a transitional government.
More than half of the population is in urgent need of assistance, the UN says.
An estimated 20% of inhabitants have fled their homes in the conflict which began as Seleka rebels seized power in March 2013.
This gave rise to the creation of largely Christian anti-Balaka militias and the situation descended into ethno-religious violence.
The Seleka leader, Michel Djotodia, stood down as president in January as part of regional efforts to end the fighting.
Mr Kamoun was appointed by the interim president on Sunday evening.
But Seleka says that even though Mr Kamoun had served as head of the tax-collecting agency during Mr Djotodia's time in power, he was not a Seleka member.
"We have been very disappointed by this appointment. It's true that Mr Kamoun worked with former President Michel Djotodia, but Seleka is well organised; Seleka has a political branch," Seleka spokesman Capt Ibrahim Nedjad said.
The rebels accused President Catherine Samba-Panza of not consulting with them before choosing Mr Kamoun.
However, Capt Nedjad said Seleka's leaders were still committed to the peace accord.
Both sides in the conflict have been accused of war crimes such as torture and unlawful killing.
Some 7,000 international peacekeepers deployed to the country have struggled to stem the violence and revenge attacks.