Bamako - Tuareg rebels in northern Mali attacked the positions of a pro-government militia on Monday, in fighting that is undermining government attempts to pacify the region, sources from both groups said.Secessionist Tuaregs signed a peace agreement in June that Western countries, including France, hope will allow the Malian army to focus on stamping out Islamist groups, some of them linked to al-Qaeda.But tensions have been rising again, and neighbouring Niger is due to host talks to ease the situation on Wednesday.A spokesperson for the Platform, an alliance of pro-government groups, said fighters from the Tuareg Co-ordination of Azawad Movements (CMA) had attacked two Platform positions in the early morning, in the third day of clashes."I think that they are looking for a pretext to boycott the meeting in Niamey by saying there are clashes in the north," said Fahad Ag Almahamoud, a leader of the Gatia militia, which belongs to the Platform.TalksHe said his group had not suffered any casualties in the fighting, which took place on two fronts near the towns of Anefis and Amassine in the northern Kidal region from around 06:00.Heavily armed CMA fighters aboard pick-up trucks raced out of the town of Kidal, the separatists' main stronghold, in the direction of the fighting early on Monday, a Reuters witness said.CMA spokesperson Almou Ag Mohamed said the Tuareg rebels had launched Monday's attacks only after Mali's UN peacekeeping mission failed to prevent Platform fighters making incursions into CMA-held areas.He said the CMA was unlikely to attend the talks in light of the violence."The planned talks in Niger are precisely aimed at preventing what is happening this morning," Ag Mohamed said. "I don't see any point to talks in Niger or anywhere else before we are able to calm the situation on the ground."Mali is seeking to break a decades-long cycle of Tuareg uprisings.Most recently in 2012, Tuareg rebels formed an alliance with Islamist militant groups and seized the desert north, prompting a French-led intervention that scattered the Islamists but failed to eradicate them.Now, Islamist violence is once more on the rise and expanding further south, putting more pressure on the government to defuse tension with the Tuaregs.