MEXICO CITY The State Department advised Americans this week to defer "nonessential travel" to vast stretches of Mexico, warning that 14 of the country's 31 states are so dangerous that visitors should avoid them if at all possible. For four other states, it counseled caution or extreme caution.

The travel warning is broader, more detailed and more alarming than the previous one for Mexico, issued in April.

The new warning became public as Mexican troops announced Thursday that they had seized 15 tons of pure methamphetamine outside Guadalajara - an amount equal to half of all meth seizures worldwide in 2009.

State Department travel warnings are based on internal guidance that embassies and consular offices use to decide where it is safe for U.S. diplomats and federal employees to travel, so they often err on the side of caution.

Still, this one, issued Wednesday evening, is sweeping. To begin with, it warns against all but essential travel across most of the states along the U.S.-Mexican border: Tamaulipas, Nuevo Leon (except the city of Monterrey, where caution is advised), Coahuila, Chihuahua and Sonora.

Ciudad Juarez, in Chihuahua, merits "special concern," the warning says, advising that the border city "has one of the highest murder rates in Mexico" and that "three persons associated with the Consulate General were murdered in March 2010" there.

Moving south, also on the no-go list for all but essential travel: Sinaloa (except the Pacific Coast resort of Mazatlan), Durango, Zacatecas, Aguascalientes and San Luis Potosi, where two U.S. Immigration and Customs Enforcement agents were ambushed and one was killed a year ago.

This means a visitor who wants to drive from the U.S. to Mexico City has no viable route that would be in accord with the guidelines.

Some of the State Department's advice can be chilling. For example, it warns travelers to avoid much of the southern Pacific states of Nayarit and Guerrero, except for the popular beach resorts of Riviera Nayarit, Ixtapa, Zihuatanejo and Acapulco. But watch your step even there, the department said: "In Acapulco, defer non-essential travel to areas further than 2 blocks inland of the Costera Miguel Aleman Boulevard, which parallels the popular beach areas."

The advisory does note that "millions of U.S. citizens safely visit Mexico each year for study, tourism, and business, including more than 150,000 who cross the border every day." Still, it says, U.S. travelers should be aware of Mexico's efforts against "TCOs (Transnational Criminal Organizations) which engage in narcotics trafficking and other unlawful activities" throughout the country.

Where to go? Much of the Yucatan Peninsula is free of murder and mayhem. No advisory is in effect for the states of Chiapas, Tabasco, Campeche, Yucatan and Quintana Roo. Good to go, too, are the popular art and food destinations of Oaxaca and Puebla. Also on the safe side of the ledger: Mexico City.