At least 27 people, including four suspected Boko Haram Islamist fighters, were killed and 100 others were injured on Monday in two attacks in Chad's capital, N'Djamena, which the government blamed on the Nigerian militant group.
The attacks, which included at least one suicide bomb, are the first of their kind in Chad, an oil-producing nation and a major Western ally which has spearheaded offensives on al Qaeda-linked groups in Mali and on Boko Haram in neighbouring Nigeria.
"Boko Haram is making a mistake by targeting Chad," Communications Minister Hassan Sylla Bakari said on state television. "These lawless terrorists will be chased out and neutralised wherever they are."
Bakari did not give further details but Interior Minister Abderahim Bireme Hamid told Reuters earlier that there had been at least one suicide attack at police headquarters.
One witness at the central police station told Reuters by telephone that he had seen three bodies on the ground. Photos circulated on Twitter of several blood-stained bodies and damaged motorbikes reportedly used in the attack.
Chad has lost dozens of soldiers fighting in northern Mali and in northern Nigeria. The first known attack by Boko Haram on Chadian soil took place in February on the shores of Lake Chad and has been followed by a handful of other isolated incidents.
However, despite threats by Boko Haram leader Abubakar Shekau to strike at Chad in relatiation for its leading role in a regional offensive against the group, N'Djamena had escaped attack so far.
The riverside city on Cameroon's border is the headquarters for a regional taskforce grouping troops from Nigeria, Chad, Niger, Cameroon and Benin to fight Boko Haram.
It also hosts Barkhane, a 3,000-strong French mission set up to fight terrorism across the Sahel-Sahara territorial band.
One foreign security source had earlier put the death toll more than 40, saying as many as 35 people were killed in two explosions at the police training school after an initial suicide bomb killed seven at a separate location.
The French foreign ministry condemned the incidents.
"France stands by Chad and its African partners in the fight against terrorism," spokesman Romain Nadal said.