U.S. Vice President Joe Biden said Monday that all three of Mexico's major presidential candidates share the same vision of continued cooperation with the United States.

The U.S. has enjoyed an unprecedented level of cooperation with current President Felipe Calderon, whose administration has received hundreds of millions of dollars to wage a heavily militarized fight against drug cartels. But Mexicans will choose a new president on July 1, with Calderon not allowed to run again.

Biden, on a one-day visit to Mexico before heading to Honduras, met with the three leading contenders: Enrique Pena Nieto of the Institutional Revolution Party; Josefina Vasquez Mota of the ruling National Action Party; and Andres Manuel Lopez Obrador of the left-leaning Democratic Revolution Party.

Recent polls show a tightening race with Pena Nieto ahead, followed by Vasquez Mota and Lopez Obrador.

When asked whether he had sensed any significant differences among the candidates with regards to cooperation with the United States, Biden answered simply, "No."

"I'm not being flip, but no," he said, before leaving a brief and unscheduled press conference at the end of a day of meetings.

Calderon's allies have accused Pena Nieto's PRI party of maintaining ties to drug-traffickers and wanting to relent in the fight against cartels. Drug-related violence has killed at least 47,515 people in Mexico from December 2006, when Calderon launched his first anti-cartel offensive, through September 2011.

Pena Nieto said he told Biden that the PRI, which ruled Mexico for more than 70 years before being ousted by the PAN, is committed to the fight against organized crime.

"The discussion is not whether we should our shouldn't fight against it but what we can do to achieve better results," he told reporters.

Lopez Obrador, the third place candidate, said that in his meeting with Biden he suggested "a new bilateral relationship with the United States based on cooperation for development."

"The problems with crime and lack of safety have their origins in the lack of welfare, and that is why it is very important that in bilateral relations, priority be given to development," said Lopez Obrador, "so that there are jobs, welfare and we can put the country on the right track and be able to decrease migration."

At a meeting earlier in the day, Calderon asked Biden for Washington to do more to halt the flow of weapons and drug money into Mexico.

Mexico's president "repeated the urgent need to strengthen actions against the trafficking of weapons into our country and money laundering," his office said in a statement.

Biden said that even in the absence of an assault rifle ban, President Barack Obama's administration was doing as much as it could to stop the flow of arms by conducting inspections of border checkpoints and requiring reporting of multiple sales of large weapons.

Biden's trip takes place amid unprecedented pressure from political and business leaders to talk about decriminalizing drugs. The presidents of Costa Rica, Guatemala, El Salvador, Colombia and Mexico, all grappling with the extremely violent fallout of a failing drug war, have said in recent weeks they'd like to open up the discussion of legalizing drugs.

Biden said the Obama administration remains strongly against drug legalization, but added that countries facing a spike in drug-related violence always ponder the question.

"It is a totally legitimate debate," he said. "The debate always occurs in the context of serious violence."

Calderon and Biden also spoke about the need to address money laundering on both sides of the border.

The Mexican government's statement said the two leaders "reaffirmed the commitment of their government to consolidating shared responsibility, confidence and mutual respect, as the basis of cooperation in all fields."