At least 17 persons, including three policemen, were killed in heavy clashes between the protesters and police in Kinshasa, the capital of Congo, the country's Interior Minister has said.Several banks have been burned, said Evariste Boshab, the Interior Minister of Congo, Xinhua news agency reported.Police on Monday fired teargas to disperse protesters who marched in the capital against President Joseph Kabila's perceived step to extend his mandate, demanding that presidential elections be held on time.Heavy columns of smoke were seen in many areas in the capital and in some spots heavy clashes were witnessed as protesters threw stones at police who in turn fired teargas to disperse the crowd.Burnt tires were seen on the streets in the capital as several streets and avenues were blocked.A police officer told Xinhua earlier on Monday that the opposition protesters did not respect the engagements of itinerary as agreed by the authorities, and that the police were right to resist.The country is scheduled to hold its presidential election on September 20. However, the electoral commission said the election has to be postponed until a voter registrar is completed, which the opposition rejects.