Nairobi - Kenya police used tear gas Monday on opposition supporters in the capital calling for electoral reform, while human rights groups said police killed dozens of people who protested after August's now-annulled presidential election.Amnesty International and Human Rights Watch said as many as 67 people died across the East African nation after President Uhuru Kenyatta's re-election was announced. The Supreme Court later nullified the vote, citing irregularities, and a new election is October 26.Researchers from the two groups interviewed 151 victims, witnesses, police and others in Nairobi's low-income areas known to be opposition strongholds. People said police pursued them, kicking down doors and shooting and beating some to death.The report said security agents carried out operations in Mathare, Kibera, Babadogo, Dandora, Korogocho, Kariobangi and Kawangware slums between August 9 and 13."This deadly use of excessive force has become a hallmark of police operations in Kenya and must be decisively stopped before the next election takes place," said Michelle Kagari, a deputy regional director with Amnesty International.National police spokesperson George Kinoti rejected the report, describing it as "sensational" and based on "falsehoods."Opposition leader Raila Odinga, whose legal challenge of vote-rigging had led the court to nullify the election, later withdrew his candidacy for the new vote. He said his calls for reforms of the electoral commission have been ignored, and he called for supporters to hold daily protests this week.The government has banned protests in the business districts of Kenya's three largest cities. Protests continued on Monday in Nairobi as police prevented opposition supporters from entering the central business district.