NDJAMENA, Chad — The president of Chad died of wounds sustained in clashes between insurgent forces and government soldiers a day after winning re-election this month, news agencies reported on Tuesday, citing the country’s armed forces.

An army spokesman appeared on state television on Tuesday to inform the nation that the president, Idriss Déby, who had ruled Chad for more than three decades, was dead, according to the news outlets.

Mr. Déby, 68, had been on the front lines in the north of the central African country, directing the fight against a rebel incursion. On the same day as the presidential election, April 11, rebels crossed the northern border from Libya.

He was due to give a victory speech on Monday, but his campaign director said that he had instead visited Chadian soldiers battling insurgents advancing on the capital, Ndjamena.

“The candidate would have liked to have been here to celebrate,” the campaign director, Mahamat Zen Bada, had said, according to local news reports. “But right now, he is alongside our valiant defense and security forces to fight the terrorists threatening our territory.”

Over the three decades since Mr. Déby seized power, he faced a number of challenges to his rule. Rebels reached the capital in 2006 and 2008. The president’s forces fought them off, with the “discreet” support of France, according to academics focused on Chad.

But in 2019, when Chad asked the French force in the Sahel region for help in dealing with another incursion, Paris was less discreet about the support, and obliged by launching a series of airstrikes on the rebels.

Jean-Yves le Drian, the French foreign minister, told Parliament at the time, “France intervened militarily to prevent a coup d’état.”

Mr. Déby was re-elected largely on the promise of restoring peace and security to a country gripped by years of violence instigated by insurgent groups. Tensions rose in the days before the latest elections, but officials urged calm.

On Monday, security forces and armored vehicles were posted to Ndjamena’s streets, prompting residents of the capital to fill up their tanks with gas, pick up their children early from school and hunker down at home. Chad’s communications minister had called for calm and wrote on Twitter on Monday that the presence of the security personnel had been “misinterpreted.”

The minister, Chérif Mahamat Zene, added, “There is no special threat to be afraid of.”

Mahamat Adamou reported from Ndjamena, Chad, and Ruth Maclean from Lagos, Nigeria.