An attack on the office of Chad's ANSE internal security agency in the capital N'Djamena has killed several people, the government has said.

Blaming the overnight assault on activists from the opposition Socialist Party Without Borders (PSF), headed by Yaya Dillo, the government said on Wednesday that "the situation is now completely under control" and "the perpetrators of this act have been arrested or are being sought and will be prosecuted".

The attack came after a party member was arrested and accused of an "assassination attempt against the president of the supreme court", its aid.

Dillo is a fierce opponent of Chad's transitional president, his cousin Mahamat Idriss Deby Itno. He denounced the attack against the Supreme Court president as "staged".

The ANSE attack comes a day after the announcement that Chad will hold a presidential election on May 6, which both Mahamat Deby Itno and Dillo intend to contest.

Mahamat Deby Itno took power in Chad after his father, Idriss Deby Itno, was killed while fighting rebels in 2021, after ruling the desert nation for three decades.