Hillary Clinton and Mexican President Felipe Calderon met in Mexico City
US Secretary of State Hillary Clinton says the US must take part of the blame for drug-related violence in Mexico.
Speaking as she arrived in Mexico, she said America's appetite for drugs and its inability to stop arms crossing the border were helping fuel the violence.
Her two-day visit comes a day after the Obama administration announced new measures to boost border security.
Some 8,000 people have died in drug-related violence in Mexico over the past two years.
MEXICO: FAILED STATE?
Enrique Krauze, historian and editor of Letras Libres, Mexico
A widespread idea, especially in the US, is that Mexico is, or is on the verge of becoming, a "failed state". This is not only wrong but a caricature of reality.
It is true that Mexico has a serious problem now in the progress of the war, a just war, unleashed by the Calderon government against the well-armed, vicious and extremely wealthy drug lords of Mexico.
But Mexico is a country with very strong institutions, made even stronger by the birth of true democracy in 2000, when the 70-year one-party rule of the Institutional Revolutionary Party ended.
We're a country that has overcome a number of serious crises: financial, governmental and electoral, and we have emerged stronger in every case because of our effective responses.
This war can only be won by reducing the range of the drug gangs and the flow of illegal guns from, and demand for drugs within, the US.
Mexico as a nation does not live in fear but we are deeply worried. The country will not collapse but Mexico and the US have to work together on these problems. There is no need for despair, but for action, in both countries.
A version of this commentary appeared in the New York Times. Translation by Hank Heifetz
On Tuesday, the White House unveiled a $700m (£475m) strategy that includes boosting security on the border, moves to stem the flow of illegal guns and drug profits from the US into Mexico, and steps to cut domestic drug consumption.
Speaking to reporters accompanying her to Mexico City, Mrs Clinton said: "Our insatiable demand for illegal drugs fuels the drug trade.
"Our inability to prevent weapons from being illegally smuggled across the border to arm these criminals causes the deaths of police officers, soldiers and civilians.
"I feel very strongly we have a co-responsibility."
She also acknowledged that US efforts to ban drugs had so far been unsuccessful in stopping the narcotics trade.
"Clearly, what we have been doing has not worked and it is unfair for our incapacity... to be creating a situation where people are holding the Mexican government and people responsible," she said.
The BBC's Stephen Gibbs in Mexico says these points have been repeatedly made by Mexico, which sometimes sees itself as the setting for an American-financed and -armed war.
In a joint news conference with Foreign Minister Patricia Espinosa in Mexico City, Mrs Clinton stressed the importance of working together to build a "common future".
Hillary Clinton: The US must "reduce demand for drugs in our country"
Mrs Clinton said discussions with Ms Espinosa had been very productive and praised Mexican President Felipe Calderon for his "great courage" in tackling organised crime.
"The criminals and kingpins spreading violence are trying to corrode the foundations of law, order, friendship and trust between us," she said. "They will fail."
Mrs Clinton said the Obama administration, working with the US Congress, intended to pledge $80m (£55m) to help Mexico buy Blackhawk helicopters.
More agents will be sent to patrol America's southern border with Mexico
"These aircraft will help Mexican police respond aggressively and successfully to the threats coming from the cartels," she said.
Mrs Clinton also spoke about the importance of trade between the two nations, as they sought recovery from the global economic crisis.
Immigration, climate change, energy issues and security were also on the agenda for the trip, she said.
Asked about a dispute between the two nations which began after the US stopped a pilot scheme which allowed Mexican trucks to use roads in the US, Mrs Clinton said only that she was aware of the dangers of protectionism.
Mexico said the decision earlier this month violated a free-trade deal between the countries and retaliated by imposing higher tariffs on some 90 American exports.
The BBC's James Coomarasamy spoke to Janet Napolitano about US- Mexico security
Mrs Clinton's trip is the first in a series of visits by high-level officials, including Homeland Security Secretary Janet Napolitano and Attorney General Eric Holder, before President Barack Obama himself visits Mexico in mid-April.
Ms Napolitano told the BBC on Wednesday that there had been a significant escalation of violence in Mexico, in part because of US efforts to clamp down on trafficking routes.
But, she said: "The most important thing is that the federal government of Mexico is now battling these cartels, and they weren't in the past. And as a result the violence between the cartels and the government of Mexico has really increased."
On Tuesday Mr Obama said: "We need to do more to make sure that illegal guns and cash aren't flowing back to the cartels.
"That's part of what is financing their operations. That's part of what is arming them."
Mexican authorities announced on Wednesday that soldiers had detained one of the nation's alleged 37 top drug-traffickers.
Hector Huerta Rios, said by the authorities to control the Monterrey operations of the Beltran Leyva cartel, was named on a "most wanted" list issued by the attorney general on Monday.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.