The African Union on Thursday called for a "democratic transition" within 18 months in Chad, where a junta took charge in April pledging just that after veteran ruler Idriss Deby Itno died fighting rebels.
The new junta, headed by Deby's four-star general son Mahamat, has appointed a transitional civilian government and promised to hold elections within 18 months.
The African Union underscored "the absolute need for a transition towards a democratic regime to be achieved within 18 months", in a statement issued in French.
"Free, fair and credible" elections must be held, the AU said, adding it "categorically rejects any form of extension of the transition period".
The union also renewed its "total rejection" of a change of government outside the constitution.
But it allowed for mitigating circumstances in Chad, noting the country was "confronted with serious attacks" as well as mercenaries from Libya fighting with the rebels and Islamist "terrorists".
The junta, which can boast one of the region's finest military forces, has declared victory after a month-long operation against rebels, claiming to have killed several hundred in the northwest of the Sahel country.
Fighting erupted on April 11, the day of a presidential election that returned the long-serving incumbent Idriss Deby Itno to power.
But Deby senior, who led the country for three decades, was killed on April 19 fighting against the Front for Change and Concord in Chad (FACT), a large armed group with a rear base in Libya.
His 37-year-old son immediately assumed control, setting up a Transitional Military Council (CMT), dominated by old regime stalwarts, on April 20 -- the day his father's death was announced.
The AU urged the new authorities to start work on a new constitution and quickly make good on promises to launch a national dialogue and reconciliation.
Ensuring human rights, freedom of expression and of assembly should also be prioritised, the union said.
Anti-junta protests broke out almost immediately but have been brutally quashed, resulting in several deaths and hundreds of arrests.
The elder Deby systematically banned protests during his 30-year rule.