For the Obama White House, pondering how to reshape the Bush administration's war on drugs, the concerns presented by the deepening crisis in Mexico are twofold.

    The first was highlighted by the chief of staff, Rahm Emanuel, talking about US-Mexican counter-narcotics co-operation. "They want to clearly stop the guns from the United States going south. We want to stop the drugs coming north," he said.

    The second concern is about another equally pernicious commodity migrating north: the violence. The announcement last month that 730 people had been arrested across the US following a 21-month investigation into Mexico's Sinaloa drug cartel confirms suspicions that the cartels are taking root in the US.

    A succession of drug-related incidents has fuelled concerns. In January a man was kidnapped outside his home in suburban Phoenix, Arizona. Initially, his family denied anything was wrong. Later, they admitted he was involved in a drugs deal gone sour and his captors were demanding $150,000 (£106,000) .

    Within two days he had been freed with the help of Arizona's recently formed kidnap unit, set up in response to the increase in ransom cases. Last year Phoenix police received 366 kidnap-for-ransom reports, a figure they estimate represents half of the true total.

    Further east in Texas, governor Rick Perry has called on the government to send 1,000 additional troops to help police the border. "I don't care whether they're military troops, or they're national guard troops or whether they're customs agents," he said. Noting the proximity of one of the centres of violence, Ciudad Juárez, Perry admitted he was concerned. "One of the deadliest cities on the north American continent," he said. "Darn tootin' it concerns us."

    Obama was briefed on Friday by the chairman of the joint chiefs of staff, Admiral Mike Mullen, who compared the challenge in Mexico to that of dealing with insurgents in Iraq and Afghanistan. America, he said, was ready to provide the kind of "intelligence support, capabilities and tactics that have evolved for us in our fight against networks in the terrorist world. There are an awful lot of similarities."

    The other crucial tie between the two neighbours is weaponry. Mexican authorities say they seized 20,000 weapons from the drug cartels last year. With the purchase of firearms difficult in Mexico, authorities conclude that most of the weapons came from the US.

    The US bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) estimates that 90% of firearms seized in Mexico come from north of the border. Of the 2,400 weapons traced back to the US, 1,800 came from dealers in the four US border states, where more than 6,500 gun dealers operate.

    The scale of the arms trade can be shocking. On 7 November last year, Jaime González Durán - known as El Hummer - a leading member of a Mexican drug cartel, was arrested in Reynosa. A day earlier, police raided a safe house belonging to El Hummer and made the largest weapons seizure in Mexican history.

    Homeland security and the ATF say that the Mexican cartels bypass gun control laws in Mexico by paying US citizens to buy guns for them.

    While a drugs strategy may be difficult to elaborate on, officials believe something can be done on guns, at least. The homeland security secretary, Janet Napolitano, has instructed the customs and border protection service "to find guns going south and interdict them".