Mexican President Felipe Calderon has told the BBC the US should do more to reduce the demand for drugs that is fuelling violence in Mexico.
He told the HARDtalk programme that more should also be done to stem the flow of illegal weapons from the US.
More than 28,000 people have died in drug violence in Mexico since 2006.
Meanwhile, President Calderon and other regional leaders have urged Californian voters to reject moves to legalise marijuana in their state.
Next week Californians will vote on a measure known as Proposition 19, which seeks to legalise recreational marijuana use.
The California vote, scheduled for 2 November, was a key issue as Latin American leaders met in the Colombian city of Cartagena to discuss co-operation in tackling drug trafficking and other issues.
Mr Calderon and his counterparts from Colombia and Costa Rica, Juan Manuel Santos and Laura Chinchilla, said legalisation of cannabis in California would send a contradictory message.
"It is confusing for our people to see that while we have lost lives and we invest vast resources in the drug war, in the consumer countries they promote proposals like the Californian referendum to legalise the production, the sale and the consumption of marijuana," said Mr Santos.
President Chinchilla, in an interview with Colombian media, noted that Central America was facing a wave of drug-related violence.
"If we think that each country on its own is going to successfully face this problem, we're very wrong," she said.
Mr Calderon had a similar message, saying international organised crime was "the biggest threat to our region".
"Our biggest wish for our region is development, but our biggest obstacle is this transnational organised crime, which knows no borders, poisons our youth and damages our people through extortion, kidnapping and murderous violence. It's not possible to really face it effectively independently," he said.
Co-operation in the fight against drugs was at the centre of an interview the Mexican president gave the BBC.
He reiterated his long-standing view that the problem of organised crime would remain as long as the US remained the biggest consumer of drugs in the world.
"They (the Americans) have a clear responsibility in this because they are providing the market for the drug dealers and the criminals," President Calderon said.
"They need to do a lot more in terms of reducing the consumption of drugs and to stop the flow of weapons towards Mexico.
Mr Calderon has long argued that the rise in violence in Mexico coincided with the 2004 lapse in the US of a ban on assault weapons.
Obama administration officials have acknowledged that the US shares responsibility for the drug violence, on account of the demand for illegal drugs and its inability to stop weapons flowing south.
However, US gun rights groups question whether the US is the source for the vast majority of the illegal guns turning up in Mexico.
The majority of guns confiscated by Mexico and submitted to the US Bureau of Alcohol, Tobacco and Firearms (ATF) for tracing do originate in the US.
However, a large number of seized weapons are not sent for tracing.
President Calderon launched his crackdown on the drug cartels after taking office in December 2006, deploying thousands of troops and police.
Since then more than 28,000 people have died in drug-related violence.
Mr Calderon insisted that the war against the traffickers would be won.
"We will prevail and we will defeat the criminals," he said, adding that the surge in violence was a sign that the cartels were turning on one another.
"Weaker cartels are acting with some kind of extreme violence, desperation I could say."
You can watch President Calderon's interview with the BBC Hardtalk programme on Wednesday 27th October on BBC World News at 0330, 0830, 1530, and 2030 GMT and in the UK on BBC News Channel at 0430 and 2330 BST.
UK viewers can watch the programme online via iPlayer for the following seven days.