Suspects accused of funnelling weapons to one of Mexico's most notorious drug cartels have been arrested by US authorities in a multi-agency operation in Phoenix, Arizona.

Twenty people were arrested in an operation involving five different US law-enforcement agencies as well as Mexican authorities. The news comes a day after US Secretary of State Hillary Clinton heaped praise on President Felipe Calderón's controversial war on drugs and accepted that US drug consumption, as well as the flow of weapons south of the border, were major contributions to the violence.

The suspects are alleged to have purchased hundreds of weapons, including AK-47 rifles, from Phoenix gun shops as well as acting as "straw purchasers"--buying weapons from stores pretending they were for personal use--for sniper rifles and pistols known as "cop killers" as their bullets are able to penetrate body armour.

President Felipe Calderón's war against drugs has proved controversial with Mexicans, disappointed at the huge increase in death and violence since it began. However, the US government is keen to voice its support and this week offered $500m in aid, adding to the Merida Initiative, a $1.4bn anti-drug plan formed under the Bush administration in 2007.

"What President Calderón has done is absolutely necessary," Mrs Clinton told reporters at a press conference in Guanajuato earlier this week. “There’s no alternative. The drug traffickers are not going to give up without a terrible fight. When they do things that are barbaric, like behead people, it’s meant to intimidate.”

More than 34,600 people have died in drug-related violence in Mexico since President Felipe Calderón took power in December 2006. Just less than 15,300 of those deaths took place in 2010 alone. Mrs Clinton said: “If it was easy, it would have been done before. It is hard and carries all kinds of costs.”

President Calderón’s drug war is not popular with many Mexicans, who live with news of death and violence every single day. “Back in the day, the narcos were always very open with the public,” said Miguel Perea, a veteran journalist in Ciudad Juárez. “You would pass by their houses and there was no problem. But when President Calderón came to power, all-out war was declared against them.”

This war is thought to have exacerbated the problem, pushing the cartels further underground. The death or arrest of cartel leaders has caused many turf wars to break out, notably in the tourist resort of Acapulco which has seen a huge number of bodies found there recently as a three-way war has erupted between cartels.

The gun-runners caught in Arizona are alleged to have been working with the Sinaloa cartel, headed by Joaquín ‘Chapo’ Guzmán, Mexico’s most notorious drug lord who escaped a maximum-security prison ten years ago. Now his name cannot even be uttered on the streets of Ciudad Juárez, on the country’s northern border with the United States.

Juárez has come to epitomise Mexico’s drug wars. WikiLeaks’ revelations this week that President Calderón requested help from the US government to subdue criminal organisations in Cuidad Juárez will shock many Mexicans.

However, residents of Juárez are keen for any help they can get, as many have lost all faith in Mexican authorities. Olga Esparaza’s 16-year-old daughter went missing in March 2009, when she was 18. She has had no help in finding her daughter from authorities and has conducted much investigation herself.

She said: “To any authorities--the FBI, Interpol--please help us. The Mexican government is incompetent and does not help us with anything. It's inhumane that the authorities have not the slightest interest in finding my daughter.”

William Simmons, an academic from Arizona State University working on legal remedies for the situation in Juárez said: “We need to give more aid from the US side in terms of humanitarian assistance and infrastructure assistance but instead we give five high-powered helicopters to the Mexican military, which is just going to exacerbate the drug war.

“If either country thinks they're going to win a war of attrition against the drug cartels, they're crazy. The cartels can replace their footsoldiers and the leadership quicker than anyone can kill or arrest them.”