In an escalation of clashes between U.S. Border Patrol agents and rock-throwing smugglers, agents have begun launching pepper spray and tear gas into densely populated Mexican border neighborhoods, according to witnesses, Mexican authorities and human rights groups.

The more aggressive approach reflects the tense climate in this city’s most notorious smuggling neighborhood, Colonia Libertad, where U.S. agents say they have had to counter human traffickers’ increasingly aggressive tactics by ramping up their own use of force.

Agents have used pepper spray in the past, but usually aimed directly at the smugglers. The new tactics, which saturate large areas, have forced dozens of temporary evacuations and sent some residents to hospitals, according to witnesses.

Border Patrol officials say tear gas and pepper spray rarely cause serious injury or damage. They say that they use them against assailants trying to divert attention from border crossers by pelting agents, and that residents are not targeted.

Since Oct. 1, the Border Patrol has counted 90 assaults against agents in the San Diego area, five times as many as during the same period a year ago. Agents have suffered serious head injuries, officials say.

The acting Mexican consul general in San Diego, Ricardo Pineda, has met with Border Patrol officials to protest the aggressive use of tear gas and pepper spray, said Alberto Lozano, the consular spokesman.

“We told them the Mexican government cannot tolerate having Mexican nationals hit with these kind of devices on Mexican soil by U.S. authorities, regardless of the reason,” Lozano said.

Residents of the area’s hillside shanties and muddy streets say the Border Patrol’s measures neglect their welfare. Some agents, they say, show compassion, even apologizing for the tactics. But others are defiant and continue saturating areas despite their pleas.

“I said to the agent, ‘Put yourself in my place. I have two children,’ ” said Robis Guadalupe Argumeo, who added that her home has been gassed three times since August, most recently after a verbal exchange with an agent Saturday. “He said, ‘I’m the policeman of the world. No one can touch me.’ ”

The agent, Argumeo said, was peering over the border fence pointing his pepper-spray launcher at her house. She said that she told him, “But this isn’t Iraq, this is Mexico” but that he continued firing into the neighborhood.

The clashes are taking place east of the San Ysidro port of entry along a two-mile stretch of border where Colonia Libertad, one of Tijuana’s most densely populated neighborhoods, pushes up against the frontier.

This was once a heavily trampled immigrant-smuggling corridor where hundreds crossed nightly, but trafficking slowed considerably a decade ago when U.S. authorities erected two layers of fencing.

In recent months, however, illegal crossings and assaults have increased dramatically, agents say. Apprehensions of illegal immigrants are up 7% this year in the San Diego area, the only area on the Southwest border that showed an increase from last year.

The situation has deteriorated to the point that authorities are considering whether to add barbed wire to fencing along certain areas bordering Colonia Libertad, an option avoided in the past because of the negative symbolism.

Agents say smugglers -- by wearing cardboard shields or heavy jackets to deflect the projectiles -- long ago adapted to the original tactic of shooting pepper balls directly at them. The agents say the pepper balls, which explode on impact, don’t seem to affect some of the hardened smugglers.

Using larger quantities of pepper spray and tear gas is more likely to disrupt their operations and de-escalate violence, agents say.

Smugglers throw rocks and other objects as one way to give immigrants time to scale the fences and disappear. Agents say the attacks are highly coordinated.

Two years ago an agent fatally shot a rock thrower in Colonia Libertad, prompting protests from the Mexican government. Border Patrol officials say using nonlethal weapons is the best way to avoid deadly outcomes.

“It’s either that or you allow those people to assault our agents at an astronomical level and somebody gets killed,” said Agent Richard Smith, a Border Patrol spokesman. “The alien-and drug-smuggling organizations should be ashamed for using innocent people as shields. It just goes to show they prioritize profit over human safety.”

Some Mexican residents sympathize with the U.S. agents. Carmen Lopez, 63, scolds smugglers who climb onto her tar-paper roof to get a better view of Border Patrol activity. “The smugglers tell me, ‘We’re just trying to make a living like anyone else,’ ” she said.

But a smuggler pelted her for complaining, and she now stays inside. If anyone’s to blame, she said, it’s the Tijuana police, who should crack down; until then the Border Patrol’s tactics are justified.

“How can they be at fault? They have a right to defend themselves,” Lopez said.

Many others disagree.

In the last few weeks, there have been at least six incidents of Border Patrol agents throwing or shooting pepper spray or tear gas into the area, forcing the temporary evacuations of dozens of people, according to witnesses and others. After a canister -- possibly of pepper spray, possibly of tear gas -- exploded outside her home in late November, Marisela Arias, 19, who is four months pregnant, said she struggled to breathe and fainted.

Her husband, Miguel Arias, 23, took her to the hospital, where he vomited, he said. Their extended family of more than eight left the house until the smoke cleared, he said.

Aberto Rojas, 37, who lives a few blocks from the Arias’ home, said he had a similar encounter with the Border Patrol the next day. Agents had targeted a smuggler who was hiding behind a van near Rojas’ property. The canister they fired in the smuggler’s direction skipped on a parked car and bounced into Rojas’ car repair shop, where the gas sent him and his brother scrambling for cover, Rojas said.

Up the hill on the same day, 15-year-old Juanita Gonzalez was washing dishes when several devices exploded on her patio, sending spray and smoke through the open window, she said. Gonzalez said she fled with her baby brothers, joining several other families rushing to evacuate on the block.

“My face was burning,” said Gonzalez, who had to be helped out of the house because she was having trouble breathing. “I felt like I was drowning.”

Argumeo, the woman whose home has been gassed three times, said that after one incident, her 12-year-old son had nosebleeds for a week. Her neighbor, Ramiro Lopez, said an errant explosive shattered his car window before exploding.

The car is the least of his worries, he said. “Something has to be done -- more than anything, for the children.”

richard.marosi@latimes.com