N'DJAMENA, CHAD -- Rebels in Chad threatened to depose the son of the country's slain president after he was named interim leader of the strategic central African nation, raising the spectre Wednesday of a violent power struggle.

It was not certain how close the rebel column was to N'Djamena, the capital city of 1 million people, or whether the military would remain loyal to Mahamat Idriss Deby following his father's sudden death after three decades in power.

The rebel group that the military blamed for President Idriss Deby Itno's killing said Wednesday in a statement that they were giving his family until midnight to bury him. The fighters gave no indication of their positions after saying the day before that they were "heading toward N'Djamena at this very moment."

The group known as the Front for Change and Concord in Chad again decried Deby's son assuming the presidency. The 37-year-old army commander was chosen to lead an 18-month transition instead of following constitutional protocol after his father's death.

"We call on all justice-loving Chadians to join us in this struggle to stop our dear republic from becoming a monarchy," the statement said.

In a bid to further legitimize Mahamat Idriss Deby's position, the National Assembly president said late Wednesday that he supported the decision to bypass him and appoint the military council to lead the transition instead. The statement came amid an outcry from opposition figures who said the constitution's rules for presidential succession had not been followed.

The rebel group's claim of advancing on the capital could not be independently verified, but it created panic in N'Djamena, which another rebel group attacked back in 2008 before being repelled by government forces.

The ruling Transitional Military Council also warned that the fight was not yet over for control of Chad.

"The security situation remains highly serious given the persistence and magnitude of the terrorist threat," the council's vice-president, Djimadoum Tiraina, said, adding that the military must now "prevent the country from sinking into chaos and anarchy."

Yet even as fears mounted that the rebels could reach N'Djamena, plans moved ahead for a state funeral Friday for Deby, a key ally of former colonizer France. French President Emmanuel Macron is among the heads of state expected to attend, French officials confirmed.

The rebels, however, urged invited state leaders on Wednesday "to postpone the invitation for security reasons."

During Deby's rule, France established its regional military base in Chad to combat extremist violence in Africa. Deby also contributed invaluable troops to the U.N. peacekeeping mission in northern Mali that has sought to stabilize the country after France's 2013 military intervention to dislodge Islamic extremists from power in the north.

Human rights groups say those contributions helped to shield Deby from international criticism as his government became increasingly autocratic.

"For years, international players have propped up Deby's government for its support for counterterrorism operations in the Sahel and the Lake Chad basin and involvement in other regional initiatives while largely turning a blind eye to his legacy of repression and violations of social and economic rights at home," Human Rights Watch said in a statement Wednesday.

Earlier this month, Deby was elected to a sixth term after facing minimal opposition because several challengers chose to boycott, fearing the vote would be rigged. In a bit to thwart opposition activists, the internet in Chad was disrupted several times before and during the April 11 voting day.

Authorities now believe the rebels blamed for killing Deby entered Chad that same day from southern Libya.

Deby, a former army commander-in-chief, came to power in 1990 when his rebel forces overthrew then-President Hissene Habre. Over the years his government survived a number of armed rebellions until his death this week. An army spokesman said Tuesday that Deby was killed while visiting the front lines of the battle against the latest rebel group challenging his rule.

The rebels now aiming for the capital are led by Mahamat Mahadi Ali, a longtime Deby opponent who formed the shadowy group known by its French acronym, FACT, in 2016 after leaving another rebel group, the Union of Forces for Democracy and Development.

Until earlier this month, FACT forces had been based in southern Libya, where they claimed neutrality in the Libyan conflict. However, a recent U.N. experts' report found that FACT forces in southern Libya were guarding Libyan military bases under the command of Field Marshall Khalifa Hifter.

The circumstances of Deby's death could not be independently confirmed due to the remote location of the fighting. Some observers initially feared a coup had taken place since the military immediately handed power to his son instead of the National Assembly president.

Mahamat Idriss Deby is best known as a top commander of the Chadian forces aiding a U.N. peacekeeping mission in northern Mali. Already some in N'Djamena question whether 18 months in power will be enough for the younger Deby.

"There is a great deal of uncertainty around how events in Chad will unfold: Whether the army will stay loyal to Deby's son and continue the effort to repel the advancing rebels," said Cameron Hudson, a senior fellow with the Africa Center at the Atlantic Council.

Chadians fed up after 30 years of Deby's rule could also align with demands for a leadership change, he said.

"Either scenario presents a high risk of civilian casualties and a likelihood that fleeing civilians or soldiers could export Chad's instability to neighbouring states," Hudson said.

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Larson reported from Dakar, Senegal. Associated Press writers Sam Magdy in Cairo and Sylvie Corbet in Paris contributed.