NAIROBI (Reuters) - Kenyan police shot dead two people and wounded a third when a crowd tried to storm a police station during an opposition protest against a looming presidential vote re-run, a senior official said.  Around 20 youths attempted to take over the station during an otherwise peaceful rally in the town of Bondo in the southwest county of Siaya, forcing officers to open fire, County Commissioner Josephine Onunga said by phone.  Police also used teargas to break up small demonstrations in Kenya s three main cities - Kisumu, the capital and the port of Mombasa - defying a government ban on rallies in city centers. Hospital authorities said 20 people were injured in Kisumu, an opposition stronghold.  Kenya s supreme court nullified the presidential election in August, citing procedural irregularities and voiding the victory of President Uhuru Kenyatta. The ruling opening the way to a repeat vote on Oct. 26.  But opposition leader Raila Odinga has refused to take part, saying the re-run should not happen until wide-ranging reforms are brought in to prevent another failed vote. The election board has said the polls will go ahead anyway, pitting Kenyatta against six other candidates, none of whom polled more than 1 percent in August.  Odinga told Reuters that he might consider returning to the Supreme Court for clarification on whether the Oct. 26 poll was legal.   As far as we are concerned, that (original Supreme court) ruling is still valid,  Odinga said during a visit to London.  What we are demanding is that the electoral commission should respect the Supreme Court and carry out elections in accordance with the ruling.  He supported protesters  right to demonstrate, he said, but has so far stopped short of calling people onto the streets himself.  In Nairobi, opposition legislators were repeatedly teargassed as they tried to drive into the city center.  We are asking Uhuru s government to ... let us protest in peace and truth and we are saying we want change and we do not want Uhuru and his people,  said protester Mellen Kirumbo.  In Kisumu, protesters reacted angrily when police turned water cannon on them to prevent them from entering the city center.   Our demonstrations have a (valid) basis and are peaceful,  said Odinga supporter Hezron Tirus Aloyo.  We condemn the directive ... on the limitation of our rights to demonstrate.   The Jaramogi Oginga Odinga hospital in Kisumu, named after Odinga s father, said it had admitted 20 patients injured in the demonstrations. Three had gunshot wounds, said superintendent Juliana Otieno.  Martin Kimani, the Director of the Kenyan government s National Counter Terrorism Centre, said the authorities were trying to maintain law and order.   A lot of those provocations or demonstrations taking place are an attempt to create the appearance of a crisis,  he said.  