Mexicans dismiss U.S. plans to send National Guard troops to the border as another futile effort that will just fuel an already booming drug- and migrant-smuggling industry.

But with caravans of heavily armed Mexican soldiers racing around this violent border city — trying to regain control from feuding drug traffickers — some worry that the buildup of U.S. troops could lead to confrontations in an area where it is often difficult to tell where Mexico ends and the U.S. begins.

CountryWatch: Mexico

Tensions in both countries have been rising over increased border-area violence spawned by drug battles, a booming human-smuggling industry and recent border scuffles.

While Mexico has stepped up efforts at combating drug, weapons and people smugglers, it leaves its migrants alone; its citizens have the right to walk up to the border, and once they cross they are out of Mexican territory.

In January, Texas authorities hunting drug traffickers came across heavily armed men dressed in Mexican military garb and chased them back across the border. The Mexican government said the men were drug smugglers disguised as soldiers.

But U.S. officials say there have been less suspicious incursions. In many areas, the border isn't clearly marked, especially in remote stretches of desert from New Mexico to California where many migrants cross.

Homeland Security Secretary Michael Chertoff has estimated that Mexican soldiers cross into the United States about 20 times a year, mostly by accident. Mexican authorities sometimes complain of U.S. officials crossing the line.

While troops are common in Nuevo Laredo, much of the Mexican side isn't patrolled, aside from the occasional military checkpoints searching for drugs and weapons.

Even so, Blanca Estela Aguilar, a 24-year-old party services saleswoman in Nuevo Laredo, said she believes scuffles between the two sides are likely.

"We are going to see a confrontation between troops over there and police here," she predicted. "It could be in the long or short term, but it will happen. And many people are likely to die."

Mexican President Vicente Fox has expressed concern about the U.S. plan, telling U.S. President George W. Bush in a weekend phone call that he would like to see a more "comprehensive" reform that respects human rights and allows for the orderly, legal movement of people across the border.

Fox's government said this week it will file lawsuits in U.S. courts if Guard troops themselves arrest migrants. But presidential spokesman Ruben Aguilar said Wednesday that Mexico respects the U.S. decision to send the soldiers and that "it's not about militarizing" the border.

Roberto Madrazo, one of three main presidential candidates, disagreed.

"We aren't going to solve the migration problem with the army," he said during a campaign appearance Tuesday. "Militarizing the border seems like another bad idea by the U.S. government. It's just going to slow the delivery of a lot of goods."

Newspapers here have referred to use of the Guard as a "lite" militarization.

Ken Roth, the executive director of New York-based Human Rights Watch, told a news conference in Mexico City on Wednesday that said he was "deeply concerned about the idea of militarizing the border."

"Whenever you introduce troops — and the National Guard are troops — you risk abuse," he said. "The Bush administration has not been terribly good at giving signals to the military about the proper treatment of people in custody."

Nuevo Laredo City Council member Jose Francisco Chavira said he's considering organizing a boycott of U.S. goods to protest the plan.

"I see it as an act of intimidation, an act that is part of a plan to build a giant wall along the border, like Bush wants," he said.