CARACAS (AFP) - President Hugo Chavez challenged US President Barack Obama on Friday to prove US claims that that four senior Venezuelan officials are involved in drugs and arms trafficking, as the foreign ministry formally protested US sanctions on the officials. Washington on Thursday accused the Venezuelan officials of aiding the leftist Colombian guerrilla group FARC and put them on a list of narcotics kingpins subject to sanctions. "I challenge president Obama to show proof of this outrage," Chavez told reporters at the Miraflores presidential palace in Caracas.