KONNA, Mali (Reuters) - Omar Sangare surveyed the wreckage in his hometown of Konna in central Mali, ravaged by battles between the army and Islamist rebels, and vowed his days of living peacefully with Arabs and Tuaregs were over.
"They are traitors," said Sangare, a member of Mali's black African majority, examining the rubble of a military base. "We saw our former neighbours, people who used to live here and run shops, among the attackers. How can we trust them now?"
As Mali's army sweeps northward with French military support, retaking town after town from al Qaeda-linked rebels, they leave in their wake a simmering hatred of the lighter-skinned Arab and Tuareg ethnic groups many Malians associate with the Islamists.
In the main northern towns of Gao and Timbuktu, liberated by French and Malian forces, residents have looted the homes and businesses of Arabs and Tuaregs. Malian soldiers have also been accused of ethnic killings in some central areas of the country.
Many now warn of a ticking timebomb for ethnic reprisals as displaced black Malians take up arms to prepare for their return home. Thousands have joined militias to complete the liberation of the north and purge it of anyone linked to the rebels.
Throughout Mali, many blame the Tuaregs for opening the door to the rebels. Tuareg separatists wrested control of the north in April but were quickly pushed aside by well-armed Islamists, enriched by smuggling and kidnapping in the Sahara.
Several Islamists leaders are also well-known Tuareg tribesmen, particularly in the Ansar Dine group. The other two main factions - al Qaeda's north African wing AQIM and its splinter group MUJWA - are packed with Arabs from Mali and neighbouring Mauritania and Algeria.
The conflict has reawakened centuries-old racial tensions in the land-locked nation. The majority of Mali's 15 million people are from the Mande, Peul and Songhai ethnicities, dwarfing the 10 percent of the population that are lighter-skinned Tuaregs and Moors, mostly inhabiting the desert north.
Tuareg nomads have long used Songhai slaves, known as "bella" in the Songhai language - a practice some rights groups and Malians say continues to this day, feeding resentment.
At a camp outside the central Malian town of Sevare, about 1,000 men - most refugees from the north - are training to help hunt down Islamist fighters. Dressed in shabby makeshift uniforms, the militia members march up and down a packed-dirt courtyard.
With only a handful of rusty Kalashnikov assault rifles and some rocket-propelled grenades, they are ill-equipped for combat against the battle-hardened Islamists. But their leader, Ibrahim Diallo, inspecting their lines, says they could help the army weed out "infiltrators" who helped rebels seize their hometowns.
"We're ready to fight, something we demanded since the day our country was targeted by Ansar Dine," said one young militia member, Issouf Ah Aguissa, standing on the parade ground. "We're not waiting for the army to accept taking us on board."
The issue is an explosive one for Mali's army, a poorly equipped and demoralised force. It is trying to recruit and train new troops, with EU backing, while coming under mounting pressure from France to prevent rights abuses.
The Paris-based International Federation of Human Rights has alleged that soldiers have killed at least 11 people in Sevare since interim President Diouncounda Traore, installed after a military coup last year, gave the army sweeping emergency powers in early January. It called for an inquiry.
In Sevare, Captain Faran Keita said militia members were expected to make up less than half of new recruits as Mali's army rebuilds. None have yet been brought in.
"We will not just throw them into the fight," Keita said. "If they want to fight alongside the Malian army, they will need to avoid making that kind of trouble."
Amid fears that ethnic reprisals could cast a pall over France's successful military campaign in Mali, French Prime Minister Jean-Marc Ayrault called on Monday for a quick deployment of international monitors to Mali.
But rights groups warn that the risk of reprisals comes not just from the militias but the broader population.
By banning music and cutting thieves' hands off, Islamists inspired deep hatred in north Mali's residents, mostly followers of moderate Sufi Islam. In acts reminiscent of the Taliban in Afghanistan, Islamists bulldozed sacred mausoleums and burned some ancient manuscripts in the desert town of Timbuktu.
"Now that the north is being retaken, the risk of ethnic reprisals is even higher," said Corinne Dufka of Human Rights Watch, who has tracked ethnic tensions since the uprising began.
"The presence of the French forces has a mitigating effect. They should continue to monitor, advise and be ready to act to protect civilians if necessary."
The feeling of suspicion among Mali's population is being fuelled by widespread insecurity after Islamist fighters have abandoned towns across central and northern Mali in the past week, ditching their flowing robes and shaving their beards to melt into the local population.
Around the central Malian town of Diabaly, authorities have set up a network of informants to watch for any strangers.
"We've been getting good intelligence," said Seydou Traore, the prefect of the central Niono region, saying several arrests had been made after residents called with information.
"We are not asking people to target Arabs and Tuaregs blindly, but if someone arrives that is not known by the population, we need to know about it here," he said. "I have asked the population not to take justice into their own hands."
Additional reporting by Cheick Diouara and Adama Diarra; Editing by Daniel Flynn and Pravin Char