Nairobi - Kenya's presidential candidates dove into a final day of campaigning Saturday before Tuesday's narrowly contested election as many worried that the vote could turn violent. The main opposition party said an American and a Canadian who were assisting with its campaign had been detained.President Uhuru Kenyatta again faces longtime opposition leader Raila Odinga. Kenyatta is the son of Kenya's first president; Odinga is the son of the country's first vice president.Recent elections in the East African commercial hub have been hotly contested, and more than 1 000 people were killed in post-election violence a decade ago. Former US Secretary of State John Kerry is among the thousands of expected election observers this time around.Some in the nation of 44 million people have been leaving the capital, Nairobi, because of the threat of chaos, while many are simply going home to vote.The torture and killing in recent days of a key election official in charge of the electronic voting system has some concerned about the possibility of vote tampering.On Saturday, Kenya's main opposition party said an American and a Canadian who were assisting its campaign were taken from their homes on Friday and detained.James Orengo, a senior member of the opposition National Super Alliance, said the detentions occurred at around the same time that armed and masked police raided an opposition vote counting center, intimidating workers and seizing equipment.A police official said immigration officials were holding the American and the Canadian at Jomo Kenyatta International Airport in Nairobi. The official spoke to The Associated Press on condition of anonymity because he was not authorized to speak with the media.