* Gunfire rings out across northern town hours after raid
* Resident says troops hunt for attackers
* Bombing underscores lack of security as U.N. force deploys (Adds death of child, number of bombers)
By Adama Diarra
BAMAKO, Oct 23 (Reuters) - A suicide blast killed two Chadian troops from the U.N. mission in Mali and injured six other peacekeepers in an assault on a checkpoint at the entry to the northern town of Tessalit on Wednesday.
Hours after the late-morning raid, which also killed a child, gunfire rang out across the desert town as Chadian and Malian troops hunted down other attackers believed to have been dropped off before the explosion, officials said.
The firing had stopped and Tessalit was calm by late evening.
No group claimed responsibility for the raid, but al Qaeda-linked Islamists, who occupied northern Mali last year, have carried out a number of suicide attacks on northern towns in recent months since they were scattered by a French offensive launched in January.
Olivier Salgado, spokesman for the U.N. mission in Mali to take over security from French troops, said the bomber drove an explosives-laden vehicle to the checkpoint before blowing himself up.
"The provisional toll is two dead and six injured," he said.
Mali's defence ministry later said four bombers took part in the raid and all died. One child was killed and another injured, it added.
Gunfire continued into the afternoon, according to another U.N. official, who asked not to be named.
Ibrahim Ag Mohamed, a Tessalit resident currently in Bamako but in touch with people on the ground, said Malian, Chadian and French forces hunted attackers in the town.
A spokesman for Serval, France's military force in Mali, said French aircraft had been sent to evacuate the wounded, and some troops were embedded as liaison officers with Chadian troops in the town. No French troops were injured, he added.
The spokesman for U.N. Secretary-General Ban Ki-moon condemned Wednesday's incident.
"This attack will not deter the determination of the United Nations to support the restoration of security, stability and sustainable peace in Mali," he said.
The United Nations appealed earlier this month for more troops and helicopters for the Mali mission, which is operating at half its authorised strength of 12,600 and has already seen some Nigerian troops withdraw.
Although the French operation swiftly defeated Islamists who overran Mali's army last year, experts have warned that many may simply have gone to ground, regrouped and sought opportunities to strike as France reduces it presence.
Bert Koenders, head of the U.N. mission, said attacks on the northern town of Gao and near Timbuktu in recent weeks were a "wake-up call" to the challenges remaining.
Mali imploded last year when Tuareg separatist rebels took up arms in the desert north, triggering a coup by soldiers angry over the government's handling of the rebellion.
Islamists took advantage of the chaos and seized the north, stoking fears in the West that the zone would become a launch pad for militant attacks and safe haven for criminal gangs operating alongside the various rebel groups.
Ibrahim Boubacar Keita, Mali's new president, must juggle restoring a shattered army and national pride while seeking to secure lasting peace with the Tuareg rebels who did not join the Islamists and are seeking a political deal. (Additional reporting by Tiemoko Diallo in Bamako and Michelle Nichols at the United Nations; Writing and additional reporting by David Lewis; editing by Mike Collett-White)