Chad’s president, Idriss Déby, has died from wounds sustained in combat, the country’s military has said, sending shockwaves through the region as rebel forces continued to advance on the capital N’Djamena. The extraordinary announcement of the 68-year-old’s battlefield death on Tuesday came days after an election in which he won a sixth term in office, extending his 30-year, increasingly authoritarian rule. Some observers fear there could be extensive fighting in the strategically important central African country before a stable political settlement is reached. Reports from N’Djamena suggest parliament has been dissolved and the government replaced by a transitional military council led by Déby’s 37-year-old son, Mahamat Idriss Déby Itno, a general. In a statement on national TV, the army spokesperson Azem Bermendao Agouna issued a call for “dialogue and peace … to all Chadians in the country and abroad in order to continue to build Chad together”. “The national council of transition reassures the Chadian people that all measures have been taken to guarantee peace, security and the republican order,” he said, surrounded by officers. But the rebel Force for Change and Concord in Chad (Fact) rejected the transition plan, saying in a statement: “Chad is not a monarchy. There can be no dynastic devolution of power in our country. “The forces of the Front for Change and Concord are heading toward N’Djaména at this very moment. With confidence, but above all with courage and determination.” The unrest has raised alarm in western countries, which saw Déby as an important ally in the fight against Islamist extremist groups, including Boko Haram in the Lake Chad Basin and groups linked to al-Qaida and Islamic State in the Sahel. His death underlines the growing instability of the Sahel region, where a complex combination of economic, social, political and environmental factors is fuelling a series of crises. Déby, who often joined soldiers on the battlefront in his military fatigues, had visited troops on the frontline on Monday after fast-moving columns of Fact fighters crossed the northern frontier from their base in Libya and advanced south towards N’Djamena. “Marshal Idriss Déby Itno, as he did each time that the institutions of the republic were gravely threatened, took control of operations during the heroic combat led against the terrorists from Libya. He was wounded during the fighting and died once repatriated to N’Djamena,” Bermendao said. Regional diplomats and security officials said that, though details were unclear, it appeared the rebels had been stopped on Sunday by a government counter-offensive bout 200km north of the capital and forced to retreat. The most recent information on Tuesday night was that the rebels had started to advance again once the news of Déby’s death was confirmed, the officials said. Though they remain many hundreds of kilometres from N’Djamena, they appear to be advancing rapidly. The army is divided and units may fight each other before taking on Fact forces, some observers said. N’Djamena remained calm on Tuesday night but very nervous. Shops were being shuttered at the central Sog Galla market “in anticipation of chaos”, one resident told the Guardian. Others in the city said many feared either an attack by the rebels or that fighting could break out between military units. Bridges and roads were jammed as some sought refuge in neighbouring Cameroon. Déby took control of Chad in an armed rebellion in 1990. He was one of Africa’s longest-ruling leaders and a close ally of western powers battling Islamist militants in west and central Africa. But he has faced repeated insurgencies in the desert north and was also dealing with rising public discontent over his management of oil wealth and crackdowns on opponents. A new constitution pushed through by Déby in 2018 would have allowed him to stay in power until 2033. Last year he took the title of Marshal and said before last week’s election: “I know in advance that I will win, as I have done for the last 30 years.” The provisional election results announced on Monday gave the incumbent 79% of the vote. A day before, the rebels said they had captured garrisons near Chad’s northern borders with Niger and Libya “without resistance”. Fact is based in Libya, where it has a non-aggression pact with Khalifa Haftar, the military strongman who controls much of the country’s east. It was founded in 2016 by disillusioned former army officers and has accused Déby of repression. Mainly made up of the Saharan Goran people, it has clashed regularly with the Chadian army. The Tibesti mountains near the Libyan frontier frequently see fighting between rebels and the army. French air strikes were needed to stop an incursion there in early 2019. In February 2008, a rebel assault reached the gates of the presidential palace before being pushed back with French backing. Some analysts believe family succession and continuing presence of the military at the heart of power may reassure nervous allies such as France and the US. “The swift announcement of the establishment of a military council and naming his son Mahamat as head of state … indicates regime continuity,” said Nathaniel Powell, author of a history of French military involvement in Chad. “This probably aims to counter any coup-making efforts from within the security establishment and to reassure Chad’s international partners - especially France but also the United States - that they can still count on the country for its continued contributions to international counter-terrorist efforts in the Sahel.” France had based its extensive Sahel counter-terrorism operations in N’Djamena. Chad, a former French colony, had announced in February the deployment of 1,200 troops to complement 5,100 French soldiers in the area. One senior regional diplomat said that the naming of Déby’s son as interim president was problematical as the speaker of parliament should have taken power on his death according to the constitution. “That in itself is a coup,” the diplomat told Reuters. “He has been grooming the son for some time. They will continue to face the rebellion. Déby had his hand in many things in the Sahel. His death disrupts things.”