SAN JOSE, Costa Rica — Powerful Mexican drug cartels are carving bloody trails through Central America, already weakened by past wars and present gang problems.

Mexico’s closest southern neighbor, Guatemala — whose government institutions are still fragile after three decades of civil war — is now seeing the brunt of the spillover from Mexico’s drug war.

Central America’s most populous nation of about 14.5 million, Guatemala declared a “state of siege” in a northern province overrun by Mexican cartels and has weighed extending the policy farther along its border with Mexico.

The December decree gave security forces expanded power to arrest and interrogate suspects. Within a week, raids led to nearly two dozen arrests and the seizure of more than 200 assault weapons and explosives, nearly 30 vehicles and five planes, Reuters reported.

People claiming to be Zetas, one of Mexico’s most powerful drug gangs, forced Guatemalan radio stations to broadcast a threat of war on society, according to the Associated Press. The alleged Zetas said that “war will start in this country, in shopping malls, schools and police stations.”

Honduras and El Salvador also deployed troops last year to thwart gang violence, as their own youth gangs grow bolder. El Salvador said last month it was bolstering security at its border with Guatemala to block a potential Zetas spillover.

Even peaceful Costa Rica, which abolished its army 62 years ago and where youth gangs are scarce, has said it needs to strengthen its national security to rout out drug gangs, including Mexico’s Sinaloa cartel, which is already operating logistical outfits in the country and across the isthmus.

“There has been organized crime in Central America for quite a long time, in some cases decades,” said Eric Olson of the Woodrow Wilson Center’s Mexico Institute in Washington, D.C.

“What changed is that the Mexican cartels that are more powerful and well developed have begun to have a presence there. Some of the conflict that has existed in Mexico plays itself out in Central America, especially in Guatemala.”

The death toll in Mexico has crept above 30,000 since President Felipe Calderon set out to crush illegal drug groups in 2006.

The deadly squeeze in Mexico, coupled with a sustained clampdown by Colombia, has resulted in a swelling of drug organizations in the isthmus between the Andean coca growing nations and Mexico.

“Both these situations in Colombia and Mexico have generated the famous balloon effect,” said Mauricio Boraschi, Costa Rica's anti-drugs commissioner. According to the balloon effect theory, cracking down on the drug trade in one region results it in springing up in another.

Costa Rica joins other Latin American governments in clamoring for more assistance from the United States, the region's top cocaine consumer, to stop the swell in drug trafficking.

In August, Washington pledged $165 million, but the region’s leaders say the funding barely helps prevent their countries from being transformed into narco states.

Boraschi said Central America is crucial to drug trafficking as Mexican gangs replace Colombian cartels to rule much of this region’s cocaine corridor. Colombian narcotics organizations, meanwhile, seem to be focusing more on European markets such as Spain, he added.

Costa Rican authorities say drug trafficking is much to blame for the country’s murder rate nearly doubling from six per 100,000 in 2000 to 11.3 per 100,000 last year — but its rate still lags far behind its neighbors, where murder rates are as high as 60 per 100,000 inhabitants.

Violence has wracked El Salvador, where local gangs reminded leaders of their brutal force in June in a public bus attack outside the capital of San Salvador that left 17 dead. When Salvadoran President Mauricio Funes moved to criminalize gang membership, the Maras and other gangs responded by strong-arming transport workers into a public transportation strike in September that paralyzed the capital for several days.

For years gangs have extorted and harassed bus drivers and other businesses.

Experts said Mexico’s drug cartels now “subcontract” local gangs including MS-13 and M-18 to carry out their dirty work.

“Youth gangs in Central America in some areas are a predominant player," Olson said. Youth gangs often control pieces of territory — for example, a roadway or coastal route — that become important when transnational organized crime groups want to move their product through the area.

In Honduras, Mexico’s deadly Sinaloa cartel has set up youth recruitment and training sites, according to a report in Honduras’ La Prensa.

In Costa Rica, according to the country’s anti-drug czar, Mexican and South American cartels outsource logistical work to “narcofamilias” — families often in poorer areas whose members turn to drug trafficking. Besides helping store and move the drugs northward, narcofamilias turn cocaine into crack for sale, fueling Costa Rica’s own drug addiction problem, Boraschi said.

Amid the spillover, presidents in the northern triangle — Guatemala, Honduras and El Salvador — are weighing a region-wide anti-gang law like El Salvador’s to stem gang violence collectively.

But Nelson Guardado, a lawmaker in El Salvador, doubts it would have much an effect.

“There are different situations in each country — each with its own laws and even different treaties signed — so making a law that’s binding would not be possible,” Guardado said.

Meanwhile, elements of martial law are back in countries where civil war is a not-too-distant memory.

“The war against drug trafficking is now the norm,” said Boraschi, who vows army-less Costa Rica won’t wage war. “Look around Central America’s northern triangle; there are three armies in the streets functioning like police — better be careful, this could mean a historic step backward.”