U.S. and Mexican authorities riding horses, all-terrain vehicles and helicopters rounded up about 500 suspected illegal aliens and drug traffickers in raids on both sides of the border, news reports said. About 50 U.S. agents swept down to the north bank of the Tijuana River's concrete-lined channel, the San Diego Union quoted U.S. officials as saying, and took about 350 suspected undocumented aliens into custody. Meanwhile, officers from city, state and federal police departments in Tijuana waited south of the border as hundreds of people fled up the south bank and through holes in the chainlink border fence, the paper said Thursday. Mexican police arrested about 150 suspected alien smugglers and drug dealers, the paper quoted Capt. Fernando Jimenez of the Tijuana Police Department as saying.