(Adds Chadian traders protest in Bangui, rebel reports) By Betel Miarom N'DJAMENA, Aug 23 (Reuters) - Chad has protested to Central African Republic after a soldier in the lawless north of the neighbouring country robbed and killed four Chadian civilians last week, its foreign minister said on Thursday. Residents and human rights groups accuse government soldiers of routinely attacking villages, looting homes and assaulting civilians, and a government official in the south of the country accused army soldiers on Thursday of spreading false rumours of rebel activity in order to extort money from civilians. Chadian Foreign Minister Ahmat Allam-Mi said the soldier had also stolen 65 million CFA francs ($134,400) and injured four others, including two women, in the attack in the Central African Republic (CAR) border town of Kabo. Chad's International Cooperation Minister Djidda Moussa Outman summoned CAR's ambassador to N'Djamena on Wednesday to express the government's condemnation of the attack, he said. The Central African ambassador pledged Bangui's support in clarifying the situation, Allam-Mi said. Chadian traders in CAR's capital Bangui shut up their shops in protest at the killings. "This is the umpteenth time we have been killed in cold blood on the pretext that we are bandits or rebels," a Chadian trader who gave his name as Abdelaziz, told Reuters in Bangui. The killing is the latest case of violence in the volatile area near Sudan's Darfur region, whose war has fuelled insecurity in northern CAR and eastern Chad. Relief workers say violence by rebels, government troops and bandits have driven some 300,000 civilians from their homes. RACKETEERING Humanitarian workers complain of attacks by government soldiers in northern Central African Republic, where insurgents are fighting a low-level war against President Francois Bozize. The government's top official in the southeastern area of Mbomou said on Thursday soldiers were spreading rumours of rebel activity to perpetuate their racketeering at road blocks. Mbomou, east of Bangui, is far from the northern rebellions, but newspapers in the capital Bangui have this week reported rebel incursions in Mbomou's main town, Bangassou. "News of rebel presence in our locality is false and was made up, honed and spread by soldiers assigned to Bangassou who have found a way to extort from the population with the help of the illegal road blocks they have set up all along our roads," Remy Semdouto, prefect of Mbomou, told state radio. Semdouto said the government had recently instructed soldiers to dismantle road blocks, where vehicles and even pedestrians are often forced to pay money to pass. "This news is being spread from Bangassou with the sole aim of making the authorities believe that insecurity is rife in the area, as a pretext for putting back these notorious barriers to confront the so-called rebels," he said. Local people and human rights campaigners accuse government soldiers -- in particular the elite guard of President Francois Bozize who seized power in 2003 and was elected president two years later -- of widespread abuse, including extortion, attacks and burning villages they suspect of helping rebels.