By Madjiasra Nako and Moumine Ngarmbassa
N'DJAMENA, July 11 (Reuters) - A man dressed in a woman's burqa blew himself up in the main market in Chad's capital N'Djamena early on Saturday, killing 15 people and injuring 80, a police spokesman said.
No group immediately claimed responsibility but Chad has blamed Boko Haram, the Islamist militant group based in neighboring Nigeria, for a series of bombings and shootings in recent weeks. Chad has been at the forefront of a regional military campaign against the group.
Police spokesman Paul Manga said 16 people including the bomber had died. Separately, police sources reported a second explosion about 30 kilometers north of N'Djamena that killed one person.
A Reuters witness saw at least 10 bodies covered in blankets lying near the southern entrance to the market place next to overturned cartons and scattered vegetables. Security forces cordoned off the area to stop people entering and searched stalls for more explosives.
Several witnesses said the bomber had tried to enter the market wearing a woman's burqa. Chad authorities banned the head-to-toe religious garment last month, citing the risk that attackers could use it as a disguise or hide explosives underneath.
"The suicide bomber was a man disguised as a woman (in a burqa). He tried to enter the market when he was intercepted by police," Manga said. "That is when he detonated the bomb."
Residents said the explosion happened at around 0830 local time (0730 GMT), during a busy period before the midday heat.
"It is terrible to live through such things during the holy month of Ramadan and right next to the main mosque of N'Djamena," Abubakar, a resident who had come to the market after hearing the explosion, said.
Boko Haram is seeking to carve out an Islamist state in northeast Nigeria and has mounted raids in neighboring Chad, Cameroon and Niger. The group has declared allegiance to Islamic State, which has declared an Islamic caliphate in territory it controls in Iraq and Syria.
Boko Haram leader Abubakar Shekau has explicitly threatened Chad in the past.
In June, two suicide attacks on police sites in N'Djamena killed at least 34 people. Since then, authorities in the central African country have made at least 60 arrests and raided an arms cache in an effort to dismantle Boko Haram's networks.
Suicide bombings occur on a nearly daily basis in Nigeria whose border is less than 100 kilometers away from N'Djamena.
A bomber blew himself up near the state security office in Nigeria's strategic city of Maiduguri on Saturday, killing at least one person and injuring four, security sources said.
Suspected Boko Haram fighters also raided the Nigerian town of Ngamdu on Friday, opening fire on residents and killing 10 people.
Chad's oil revenues have helped to finance its defense spending, and N'Djamena serves as a headquarters for an anti-Boko Haram regional force. The country also serves as a base for a 3,000-strong French mission fighting militancy in the Sahel.
France strongly condemned the market attack on Saturday. (Reporting by Moumine Ngarmbassa and Madjiasra Nako; Additional reporting by Joe Hemba in Damaturu and Lanre Ola in Maiduguri; Writing by Emma Farge and Julia Payne; Editing by Andrew Heavens and Hugh Lawson)