N"DJAMENA, Oct 2 (Reuters) - One policeman was killed and around ten people were wounded in Chad"s capital N"djamena on Saturday after police used tear gas to disperse a protest against the ruling junta that had strayed from the approved route, a police spokesperson said. Civil society coalition Wakit Tamma had asked supporters to take to the streets to denounce the Transitional Military Council (CMT), which seized power in April after President Idriss Deby was killed while visiting troops fighting an insurgency in the north. "There were clashes which resulted in around 10 minor injuries and the death of a police officer following a fall," said police spokesperson Paul Manga. Wakit Tamma accused police of using excessive force and said around 20 people were wounded, including some by live rounds. "This brutality by law enforcement officers is all the more unacceptable because the march was peaceful and moreover authorised," it said in a statement. It estimated around 1,200 people attended the protest, whereas the police said there were around 100. Deby"s death caused chaos in Chad, a key ally of Western powers in the fight against Islamists in Africa. His son, Mahamat Idriss Deby, dissolved parliament after his death and took control as head of the military council. He has promised to hold democratic elections within 18 months. Opposition politicians have denounced the move as a coup. Security forces have repeatedly clashed with protesters calling for a return to civilian rule.