Colombia is investigating instances of Venezuelan air force planes entering its airspace to cover left-wing Colombia guerrillas who were retreating into sanctuaries across the border, internal government documents obtained by United Press International show. The Colombian army is investigating more than a dozen reported Venezuelan military incursions to aid narco-guerrillas of the Revolutionary Armed Forces of Colombia, or FARC, in their decades-long struggle against Colombia's U.S.-backed government and right-wing paramilitaries. The most serious clash took place March 21. Some diplomats say Venezuelan President Hugo Chavez may want to pick a fight with Colombia to deflect the attention of his armed...