A violent drug war between the Mexican government and vicious drug gangs is escalating just over the border in Mexico — and causing concern among U.S. law-enforcement officials and lawmakers. The cartels already effectively control significant stretches on the Mexican side of the border, and now they're expanding activities on the U.S. side, including kidnapping Americans. More than 5,300 people — gangsters, soldiers, police, journalists and other civilians — have been killed this year, more than double last year's toll. Some victims have been beheaded. The Bush administration has stepped up security assistance to Mexico, but so far the aid hasn't dented the gangs' firepower, which largely depends on smuggled U.S. weapons. Some prominent foreign-policy experts say the ultimate solution is preventing drug abuse in the United States, not expanding the Mexican government's arsenal.