A leading critic of Chad's military leader, Mahamat Déby, has been killed in a shootout with security forces, officials say.

Yaya Dillo's death comes after the government blamed him for a deadly attack on the country's security agency. He denied the accusation.

On Wednesday, heavy gunfire was heard near his party's headquarters in the capital, N'Djamena.

Mr Dillo was also a cousin of President Déby, who has been in power since 2021.

Mr Déby was named by the army to succeed his father who was killed by rebels after three decades in power.

The unrest in the Central African country follows the announcement that presidential election will be held on 6 May.

These elections are intended to return the country to constitutional rule.

Before his death, Mr Dillo was widely predicted to be his cousin's main opponent in the election.

He was the leader of the Socialist Party Without Borders (PSF).

Communications Minister Abderaman Koulamallah told the AFP news agency that Mr Dillo had died on Wednesday "where he had retreated, at the headquarters of his party. He didn't want to surrender and fired on law enforcement".

The authorities said 12 others also died in the shootout.

Mobile phone and internet networks in Chad have been down since the reported attack on the National Security Agency (ANSE) headquarters.

Amaury Hauchard, a journalist based in N'Djamena, told the BBC on Thursday evening: "For 24 hours, people have not had access to the internet - only a few hotels have access."

He added that Mr Dillo's death had raised doubts about whether the election could still be held as planned

On Wednesday, Mr Dillo said the accusation he was behind the ANSE attack was intended "to make me afraid so that I don't go to the election".

The PSF denied the government's version of events, saying its members were the ones who had come under attack.

The party's general secretary told Reuters news agency that soldiers had targeted them while they were trying to retrieve the body of their colleague Ahmed Torabi.

Mr Torabi had been arrested and shot dead on Tuesday, before his body was dumped outside the ANSE building, the PSF said.

This was not Mr Dillo's first violent run-in with security forces.

When running against the current president's father, Idriss Déby, for the presidency in 2021, state forces killed Mr Dillo's mother, son and three others, the PSF said.

The party said the assailants were attempting to arrest Mr Dillo.

At the time, the government contested the PSF's death toll, saying three people had been killed.