At least 23 people have been killed and more than 100 injured in suicide attacks in the Chadian capital N’Djamena, officials say.
Attackers on motorcycles blew themselves up outside two police buildings, say witnesses.
A government minister blamed Nigeria’s militant Islamist group Boko Haram in an address on state TV, Reuters news agency reports.
The group has not said if it was behind the attack.
But it has often carried out suicide bomb attacks during its six-year insurgency in neighbouring Nigeria.
Boko Haram had “made a mistake targeting Chad”, and would be “neutralised”, said Communications Minister Hassan Sylla Bakari, quoted by Reuters, adding that four of the attackers had been killed.
Chadian forces have played a key role in helping Nigeria battle the jihadist group, and the headquarters of a regional force is being set up in N’Djamena.
The group has never targeted N’Djamena before, but this attack should not come as a huge surprise given Chad’s role in fighting the insurgency, reports the BBC’s Will Ross from Lagos.
Boko Haram gunmen have previously been active around Lake Chad close to the Nigerian border.
Video statements from the Islamist group have previously criticised and taunted Chadian President Idriss Deby.
The Nigerian army has begun moving its headquarters from the capital Abuja to Maiduguri, the capital of the north-eastern Borno state at the heart of the insurgency.
Boko Haram has lost most of the territory it had controlled following the regional offensive.
But it has continued to stage deadly attacks in Nigeria.