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 the Mexican 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.

Even when they aren’t blocking essential services to a community, the drug gangs interrupt daily life on a frequent basis with bloody bouts of violence.