The Chadian army has announced a four-star general Mahamat Kaka, son of Chad’s long-time President Idriss Déby as the country’s leader, and the dissolution of the government and parliament.
The military has also announced that elections will be held in 18 months’ time.
Experts however say the move is unconstitutional, and that the speaker of parliament should take over when a sitting president dies before organising elections.
A nightly curfew has also been imposed by the army with immediate effect, between the hours of 18:00 and 05:00.
President Déby was injured when visiting troops battling rebels who had launched a major incursion last week from their base in Libya, the army said.
The 68-year-old leader came to power in an armed uprising in 1990 and was often lauded for his efforts in fighting insurgency.
In 2020, he was awarded the highest military rank of Field Marshal because of the same efforts.
He had been set to lead the country for a sixth term after securing a huge lead in provisional results announced on Monday.
The vote earlier this month was heavily contested and the main opposition candidates had pulled out citing attacks by state forces.
President Déby had been criticised for his human rights record but is seen as a key security ally by France and other countries in the region in the battle against Boko Haram and other groups liked to al-Qaeda and the Islamic State.
Crucially Chad also neighbours Libya, Sudan and the Central African Republic which have also faced instability in recent years