Bujumbura - At least 100 rebels have been killed after a cross-border attack against the central African nation of Burundi from the Democratic Republic of Congo, a top military source told AFP Sunday.A general in the Burundian army, speaking on condition that he not be named, said the attack by the unidentified rebel group had been defeated after five days of heavy fighting in the border area north of the capital Bujumbura."After five days of non-stop military operations, the armed group which attacked Burundi has been wiped out by our security forces. In total, we killed 105 of them and captured four, out of a total of the 121 who entered Cibitoke province from the DRC," the general said."We also seized a 60mm mortar, five rocket launchers, machine guns and more than 100 assault rifles," he said, adding the Burundian army had lost two soldiers. Other military sources said around 12 soldiers were killed in the fighting.There was no further confirmation of the claim, with army spokesperson Colonel Gaspard Baratuza declining to comment officially on the fighting "while military operations in the area are still in progress”.A previous toll given on Wednesday put the toll at 35 dead, including 34 rebels and one government soldier.Burundian officials and witnesses said the group of unidentified rebels crossed into Burundi overnight on Monday from DRC's eastern Kivu region, a chronically unstable and resource-rich area that is home to dozens of rebel groups.Colonel Baratuza said troops had seized documents allowing the army to get information on the size of the force and the identity of their leaders, but he did not disclose the identity of the group.'Teach a lesson'Security forces then fought to prevent the rebels from reaching the Kibira forest, an area used in the past by rebel groups as a base to stage further attacks inside Burundi."The security forces, backed by the local population, surrounded the group in Murwi commune, and chased them without respite, giving them no time to recover or sleep," said the military source.Burundi opposition and civil society sources said they had heard reports of rebels being disarmed and then executed by shooting or with machetes, with the killings carried out by the Imbonerakure, a controversial youth wing of Burundi's ruling CNDD-FDD party. The Burundian military denied the allegations, but the senior source acknowledge the security forces - which included soldiers back from African Union operations in Somalia - wanted to "hit the rebels hard" and "teach a lesson" to other rebel groups.Previous attacks in Burundi's border region have been claimed by a splinter faction of the National Liberation Forces (FNL). The main body of FNL - a highly disciplined group notorious for singing hymns as they carried out attacks - signed a peace deal with the Burundian government in 2009 and have since become a political party.The rebels who still fight on have claimed a string of attacks in 2014, most recently in October when they claimed to have killed six soldiers, and vowed to "intensify" their raids ahead of presidential elections in June. The group, however, have denied they were behind the latest attack.Burundi, a small nation in Africa's Great Lakes region, emerged in 2006 from a brutal 13-year civil war and its political climate remains fractious ahead of the elections when President Pierre Nkurunziza, in power since 2005, is expected to run for a third term in office despite opponents' claims that that would violate Burundi's constitution.