Mexico's notoriously violent drug cartels get much of their weapons from stockpiles in Central America left over from conflicts in the region, a top US military official said Tuesday.

"Over 50 percent of the military-type weapons that are flowing throughout the region have a large source between Central American stockpiles, if you will, left over from wars and conflicts in the past," General Douglas Fraser, head of the US Southern Command, told a Senate hearing.

Fraser said last week that US authorities believed there were between 45 million and 80 million weapons circulated in Central America, much of those left over from civil wars and other conflicts.

Fraser said US authorities have "a lot of focused efforts" to limit those stockpiles to stem violence in the region. But he added that "there's a lot of funding available with these transnational criminal organizations."

Admiral James Winnefeld, head of the US Northern Command, said the Mexican cartels "are getting more and more sophisticated" but do not pose "an existential threat to the government."

Winnefeld said the Mexican government, which has been waging a bloody war against the drug cartels, has an opportunity to "turn the corner" in the fight with proper support but that the outcome "still remains to be seen."

Some 35,000 people have died in suspected drug-related violence since the launch of a Mexican government offensive on organized crime in 2006, according to official figures.