Top detective among latest of around 80 people killed since April in Tamaulipas state, after new crackdown on criminal groups

A spate of extreme violence in Mexico's north-eastern Tamaulipas state has ended the relative calm in the region where the country's drug wars began.

Officials say about 80 people have been killed in almost daily street battles. This week the state's top detective, Salvador de Haro Muñoz, was among five people killed in a shootout. Ten police officers have been arrested for allegedly leading him into an ambush.

Fourteen people were killed in one day this month in a string of gun battles between federal forces and unidentified gunmen in the city of Reynosa, across the border from McAllen, Texas.

"It's worse than ever," said a local woman who saw three shootouts on three consecutive days while visiting relatives in Tampico in early April. The woman, who asked not to be identified, said authorities did nothing to intervene beyond advising people to stay off the streets. "This is a failed state with no law and no authority."

Tamaulipas has been a focal point in the drug wars as one of the busiest places on the border for northbound drugs and migrants and southbound weapons and cash. But the latest outbreak of bloodletting has prompted fears that the region is set for a return to the worst days of 2010, when entire populations fled towns in the region to escape the violence.

Many date the start of the drug wars to attempts by the Sinaloa cartel to take over the frontier heartland of the rival Gulf cartel in 2004-5. That incursion was repelled by the Gulf cartel's enforcement wing, a group of former special forces soldiers know as the Zetas.

The region was plunged into one of the bloodiest conflicts of the drug wars when the Zetas split from their former paymasters in 2010. Large deployments by the army and navy helped to restore some kind of calm by 2012, and both the Zetas and the Gulf cartel have been weakened after leaders in both factions were captured or killed.

The state government spokesman Guillermo Martínez said this week that the resurgence of violence in Tamaulipas was the result of government successes in "squeezing" the criminal groups. "The important thing is that we are facing the problem head on," he said.

Eduardo Guerrero, a security expert, agreed that the latest spasm of violence had been triggered by recent arrests of regional Gulf cartel bosses, but said further clashes had been caused by power struggles between rival factions within the cartel, and by efforts from the Zetas to take advantage of these rifts.

"The situation in Tamaulipas is extremely complicated," he said, adding that he hoped the crisis would put pressure on the state authorities to speed up efforts to get local police forces into shape rather than relying solely on federal forces.

Mario Segura, a journalist who fled the state after being kidnapped in 2012 but who now makes periodic visits to work with victims of the violence, said that after years of intimidation, local people were starting to lose their fear of the cartels and could put further pressure on authorities to restore order. "It is not going to happen very soon but I feel that things are moving," he said.

Segura said many people seemed inspired by the example set by armed vigilantes who took on the Knights Templar cartel in the central state of Michoacán. But one resident of Ciudad Mier – a town near a strategic crossroads, where gunmen recently peppered the main hotel with bullets before clashing with soldiers – disagreed. "We know that all we can do is hide," she said. "It's been going on for so long now that I am losing hope that we will ever have peace in Tamaulipas."