MEXICO CITY (AP) — Train robberies in central Mexico are growing more violent and attracting criminals who used to steal fuel from government pipelines.

But authorities and rail lines exchanged blame Monday for the rise in robbery of merchandise from the trains.

Puebla state police said they have been asking railways for months to take steps to combat robberies, but they have failed to do so. Police say the railways don't report incidents until an average of six hours after they happen, then don't file criminal complaints and give incorrect information about freight shipments and timetables of trains running through areas known for robberies.

Police said some unionized engineers simply stop their trains on the tracks when their shifts end, making them vulnerable to attacks.

An official of Ferromex, one of the nation's leading railways, told an industry journal last week that a significant percentage of the 35 trains per day the company operates in the area around Puebla and the neighboring state of Veracruz are attacked.

"It gets to the point where you don't have the flow needed to provide an efficient service," Ferromex official Lourdes Aranda told the internet site T21. She said bandits are now using assault rifles to threaten train employees.

Train robberies have increased in Mexico, but haven't previously been so violent.

Thieves usually just stopped trains by piling logs or rocks on the tracks, and then sent throngs of unarmed people to overwhelm guards and steal grain, cement, electronics and other cargo.

But Puebla authorities say more violent people are getting into that business, as the state and federal government crack down on thieves who drill taps into government pipelines to siphon off fuel.

Police said Sunday two armed train bandits opened fire on a police patrol. One of the suspects was detained and another was killed when police returned fire. He was the second train robber killed in a firefight this month.

But it's unclear whether fuel theft has diminished, either.

Nationwide, illegal pipeline taps rose to 928 in August, the latest month for which figures are available, up from 731 in July. Puebla had the most taps of any state in the county, with 172 in August, up from 107 in July.

On average, thieves tapped into pipelines 28 times per day nationwide this year.