The attack in N'Djamena, by a man disguised as a woman in a full-face veil, came after a botched bombing in the capital of Nigeria's Borno state, Maiduguri, which killed two pedestrians.
Militant fighters on Friday night also raided the village of Ngamdu, some 100 kilometres from Maiduguri, killing 11, residents and a member of the civilian militia said.
The attacks underlined the threat still posed by the Islamists in the region, despite the authorities' claims of recent military successes and with a new regional force set to deploy at the end of the month.
Muslim-majority Chad banned the full-face veil, ramped up security measures and bombed militant positions in Nigeria last month after the first ever Boko Haram attack in its capital.
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The provisional toll yesterday was 15 dead and 80 injured, four of them seriously, said police spokesman Paul Manga. Nine of the victims were female traders and one was a police officer, he added.
An AFP correspondent there described a gruesome scene of carnage and pools of blood.
The attack in Maiduguri saw two bombers in a motorised rickshaw try to get into a busy bus station on Saturday morning. They were deterred by heavy security, however, and the attack happened nearby.
Boko Haram claimed responsibility for the attacks in Chad and Maiduguri via Twitter, according to the US-based SITE Intelligence Group, signing off as "Islamic State, West Africa province" -- the militant's self-styled moniker since pledging allegiance to the Islamic State group in March.
On June 15, 38 people were killed in a twin suicide attack at a police academy and the main police station in N'Djamena, where a French-led operation against sub-Saharan extremists is based.