CARACAS, Venezuela (Reuters) - Venezuelan President Hugo Chavez said his government will go ahead with the purchase of Spanish military aircraft and naval vessels even as he accused the U.S. government of pressuring Madrid to halt the transaction. Chavez, closely allied to U.S. foe Cuba, has stepped up military spending this year with a slew of deals for Russian automatic rifles and helicopters, Brazilian aircraft and Spanish patrol ships and aircraft. U.S. officials, who brand the leftist leader a threat to the region's stability, say they are worried some of the Venezuelan weapons could fall into the hands of Marxist...