MEXICO CITY -- Five Pemex workers went to their jobs at a government-owned gas compression plant near the Texas border six months ago and never returned. Masked men, apparently members of a drug cartel operating there, had warned employees of Petroleos Mexicanos that they were no longer allowed to enter the area.

Around the same time in May, three inspectors for Mexico's Environment Department headed into the wooded mountains west of Mexico City to investigate a pollution complaint. Their tortured bodies were found the next day. Authorities said they stumbled onto a drug lab.

With killings and disappearances to assert their authority, Mexico's drug cartels are beginning to interfere with everyday government activities in pockets of the country, keeping workers off their turf and interrupting some of the most basic services.

Not only do they maintain checkpoints and kill police or mayors to control territory, they now try to keep everyone from midlevel officials to delivery truck drivers and meter readers out of rural areas they use to transport drugs, stash weapons and kidnap victims, and hide from authorities. In the process, they are blocking deliveries of gasoline, pension checks, farm aid and other services to Mexicans.

Cartels also rob or extort people receiving government checks, as organized crime branches out from drug running into other illegal businesses.

These interruptions have even affected the U.S., as agricultural inspections at the border have slowed. The recent search for the body of a missing American tourist on a border lake was suspended under threats of drug-cartel violence and the assassination of the police commander in charge of the search.

"Everything's stopped," said Maria Luz Hopkins, a 69-year-old retiree in Tubutama, south of the Arizona border city of Nogales. "There's no construction. Nobody is working the fields because they don't have gasoline or diesel. The people that used to bring gasoline, they don't come. How can people work?"

Hopkins complained to officials in the Sonora state capitol, Hermosillo, when the government stopped delivering pension checks. She said they came last month in a convoy of about 20 heavily armed trucks after missing a bimonthly payment over the summer.

Federal officials say these are isolated incidents, and deny there is any area of the country where the government can't operate; as evidence, they point to the 2009 congressional elections and the 2010 census.

"There might have been incidents, but this doesn't mean that government business is stopping anyplace in the country," said federal security spokesman Alejandro Poire, while adding, "if and when it happens, federal forces, if need be, will be there to enforce the law and keep government business operating normally."

But in pockets along the border or in the mountains of the interior, fleeting army patrols and brief visits by census or poll workers can hardly count as government control. Even military personnel are nervous and insist on wearing ski masks to avoid identification.

For Pemex, the kidnappings are "a broad problem," says General Director Juan Suarez Coppel, much larger than one plant and growing, according to figures provided under a freedom-of-information request filed by The Associated Press. A total of 10 Pemex employees or subcontractors were kidnapped in four Mexican states in 2010, compared with only one in 2009, two in 2008 and three in 2007.

Pemex, the country's largest single industry, supplying about 40 percent of the federal government revenues, would not offer estimates on what financial losses such attacks have caused. The company could not say what happened to the victims, or how much production had been lost because of the security problems in border states such as Tamaulipas and Nuevo Leon, and the Gulf coast states of Veracruz and Tabasco.

"There have been a series of situations in the northern part of Tamaulipas state and part of (neighboring) Nuevo Leon state that have made it difficult to operate," Carlos Morales Gil, the director of Pemex Exploration and Production, said in a written reply to The Associated Press.

The problems go beyond Pemex.

Vehicles carrying the village of Tubutama's comptroller and director of public works were attacked by bandits and the officials gunned down in June. Electricity flows freely because meter readers refuse to go there, said one rancher, who asked that his name not be published because he fears for his safety near the Mexico-Arizona border.

Doctors don't show up at Tubutama's health clinic, schools closed early last year because shootouts made it unsafe to get kids to classes, and shelves of general stores are bare because suppliers won't truck in supplies to the town of 1,500.

Many townspeople have fled -- the rancher estimates 70 percent -- because they feel the government cannot protect them, as have their counterparts in Ciudad Juarez and smaller towns along the Texas-Mexico border. The federal government also stopped delivering cash under President Felipe Calderon's anti-poverty program, Oportunidades, said the rancher, whose extended family fled Tubutama earlier this year.

The Oportunidades program says it has suffered 134 robberies of town or village deliveries in the last 2 1/2 years, a loss of about 142 million pesos ($1.1 million dollars). Most robberies occur in the area known as the "Golden Triangle," where the drug-plagued states of Chihuahua, Sinaloa and Durango meet, according to the federal Department of Social Development, which administers the program.

The loss is a tiny percentage of the program total of about 25 billion pesos (about $2 billion) annually. Officials say they usually try to reschedule a new delivery within days for affected areas, where the handouts are almost the only source of cash income. But in some cases, it takes weeks.

In the border Chihuahua state that includes Ciudad Juarez, drug gangs -- and criminals working for or tolerated by them -- have grown so powerful and brazen that they rob aid checks from local farmers. Names of those receiving aid are made public as part of a federal program of transparency and accountability.

Farmers say the practice makes them targets for extortion.

Federal Agriculture Secretary Francisco Mayorga acknowledged a problem with delivering farm aid to the area.

"We are legally required to publish the names of the beneficiaries, but we unfortunately have a risk to their security," Mayorga said.

Chihuahua farm groups last month asked his department to stop the practice.

"They tell some people, 'We'll burn your ranch,' and they will tell other people, "Hey, you have children, something could happen to them ... unless you give me the money,"' said Ruben Chavez, the leader of the Unipro farm cooperative in Ciudad Cuauhtemoc, Chihuahua.

In the case of the environmental inspectors, officials are almost certain that traffickers tortured and killed them along with a local man serving as a guide after they stumbled across a clandestine drug laboratory,

Christopher Cadena, 22, was one of the five Pemex workers who disappeared in area near the border city of Reynosa. The area across from McAllen, Texas, is the center of a violent rivalry between the Gulf Cartel and Los Zetas, a brutal drug gang made up of former Mexican special-forces soldiers.

His father, who asked that his name be withheld because of threats, says the gang that kidnapped his son wanted area around the plant vacated to move drugs.

"The other four boys, my son's colleagues, had been threatened the Friday before. They had told them they didn't want to see them around there again," said the father, adding the threats were made by a men dressed in military-style shirts and pants who carried assault rifles but wore sneakers instead of boots.

"They want that corridor unpopulated," the father said. "They want to kick Pemex out."