The war on drugs just got a whole lot more warlike. Two hundred U.S. Marines have entered Guatemala, on a mission to chase local operatives of the murderous Zeta drug cartel.

The Marines are now encamped after having deployed to Guatemala earlier this month, and have just "kicked off" their share of Operation Martillo, or Hammer. That operation began earlier in January, and is much larger than just the Marine contingent and involves the Navy, Coast Guard, and federal agents working with the Guatemalans to block drug shipment routes.

It's a big shift for U.S. forces in the region. For years, the Pentagon has sent troops to Guatemala, but these missions have been pretty limited to exercising "soft power" – training local soldiers, building roads and schools. Operation Martillo is something quite different.

The news comes as two U.S. agents wounded in an attack in Mexico last week were discovered to be likely working for the CIA. The attack appears to be a case of mistaken identity after the agents fled from a Federal Police checkpoint, thinking the plain-clothed Mexican cops were cartel members. Police, seeing the agents' bulletproof SUV flee their checkpoint, presumably thought the same thing, followed them and shot up their car. The agents have now been discovered as likely working for the CIA, as one of the wounded agents' false identity was linked to a post office box in Virginia previously tied to CIA rendition flights.

The Marines' share of the operation involves chasing drug traffickers with UH-1N Huey helicopters. The Marine contingent has four of the choppers, and the Marines are carrying weapons. "It's not every day that you have 200-some Marines going to a country in Central and South America aside from conducting training exercises," Staff Sgt. Earnest Barnes, the public affairs chief for Marine Corps Forces South, tells Danger Room. Prior to the Marines' deployment, there were only a "handful" of Marines in the country, Barnes says.

However, the Marines can't technically use their guns except in self-defense, and Barnes wouldn't say whether they're authorized to pursue drug traffickers on the ground. The description of what they're doing, however, suggests that they probably can't. Instead, they'll be looking out for suspicious boats – including crude narco-submarines – and then radio the Guatemalans, who do the work seizing their drugs and arresting cartel members. That could be on rivers, or along Guatemala's two coastlines, reports the Marine Corps Times.

"Overall the Marines are there to provide aerial detection and monitoring, and aerial surveillance, and so the appropriate authorities can do their job, whether it being Guatemalan military or some other form of law enforcement agency or authority to perform their duties," Barnes says. Among the force are pilots and communication teams, as well as combat engineers to build landing sites.

On the other hand, just because the Marines may not be officially authorized to stop drug traffickers – instead only spot them – doesn't mean they won't be drawn into a conflict. The drug war is messy and involves going after criminal groups that don't for the most part wear uniforms or identify themselves as cartel members. Nor is it true to say the U.S. isn't already involved in a shooting war in Guatemala, with potentially ill consequences.

On the night of May 11, Honduran troops along with Drug Enforcement Administration agents allegedly killed two civilians – possibly four according to local accounts – including a pregnant woman. According to a report released this month by the Center for Economic Policy and Research, Honduran troops and U.S. agents seized a boat on a river containing cocaine near the town of Ahuas, when another boat – containing civilians – rammed into the first boat in the darkness. DEA agents and Honduran troops circling in a helicopter then fired on the second boat (.pdf). The U.S. has denied that any of its agents took part.

The DEA isn't a military organization, but what the Ahuas shootings represented was a military approach to the drug war gone bad. A case of mistaken identity, sure, as the mayor of Ahuas said following the shootings. But it also reflects a danger of stopping drugs at the point of a gun.

The Ahuas shooting "demonstrates the risks of flooding foreign countries with armed representatives of the U.S. government, to fight an enemy that is largely indistinguishable from the civilian population on unknown terrain," wrote Patrick Corcoran of InSight, a Latin America crime monitor. "The Ahuas shooting may not have been inevitable, but as Americans take a more hands-on role, such scandals are likely to be repeated," he wrote.

On the other hand, as Mexico's drug violence worsened, cartels like the Zetas began spilling over Mexico's southern border. Guatemala is now a base for the Zetas, who use the country's remote northern region shipment route for narcotics and weapons. In February, Guatemalan President Otto Pérez Molina said his country is "not doing what the United States says, we are doing what we have to do" – in other words, decriminalize drugs. But Molina has also emphasized cracking down on the cartels in a mano dura, or "iron fist," approach to crime.

Now, on the contrary, the U.S. hasn't gone anywhere close to suggesting drugs be decriminalized. Gen. Douglas Fraser, the head of U.S. forces in South and Central America, said last year to the House Armed Sevices Committee that "the violence continues to increase in Central America, and that's where and why we are focusing there."

That's where the Marines come in. And as far as the Zetas go, the U.S. hasn't directly confronted them with troops. Mexico City will absolutely not allow it. Guatemala is different, which means the distance between the gun barrels of a militarized cartel, and that of the U.S. military, could start to get much shorter.