President Barack Obama and Mexican President Felipe Calderon have pledged to work together to fight drug trafficking, border violence, environmental dangers and other shared challenges. The two leaders met at the country's presidential residence.

Emerging from a 1 1/2 hour meeting, Presidents Obama and Calderon announced a flurry of bilateral understandings, proposals, and pledges on a wide range of issues.

President Obama said he has great admiration for Mexico's leaders in their fierce and prolonged battle against drug traffickers. "But I will not pretend that this is Mexico's responsibility alone. The demand for drugs in the United States is what is helping to keep these cartels in business. This war is being waged with guns purchased, not here, but in the United States," he said.

Mr. Obama said he wants the U.S. Congress to ratify a treaty limiting U.S. gun exports to the Americas and continue funding for a program that would provide Mexico with military helicopters to assist in the drug war.

The president reiterated his support for reinstating the expired U.S. ban on assault weapons, but acknowledged Congressional resistance makes that unlikely. Instead, he pledged to boost enforcement of existing laws. "Trafficking illegal firearms, sending them across a border, is illegal. That is something that we can stop," Mr. Obama said.

President Calderon has repeatedly urged the United States to crack down on arms shipments south of its border, saying 90 percent of weapons in the hands of drug traffickers originate in the U.S.

The Mexican leader said the United States and Mexico must combine efforts to fight climate change and reduce carbon emissions. He also hailed what he termed the complimentary nature of the two nations' economies, saying that both can be made more competitive through cooperation and integration. To that end, he said he and Mr. Obama discussed ways to improve infrastructure along the U.S.-Mexico border to facilitate bilateral trade.

For years, Mexico has urged Washington to address the status of more than 12 million undocumented workers in the United States, more than half of whom are Mexican. President Obama reaffirmed his commitment to pursuing comprehensive immigration reform -- an initiative that appears stalled in the U.S. Congress.

"I am committed to fixing our broken immigration system in a way that upholds our traditions as a nation of laws, but also as a nation of immigrants. And I am committed to working with President Calderon to promote the kind of bottom-up economic growth here in Mexico that will allow people to live out their dreams here [in Mexico], and as a consequence will relieve some of the pressure that we have seen along the [U.S.-Mexico] border," he said.

Overall, President Calderon said his meeting with Mr. Obama was ground-breaking.

He said it was a historic event and that he is certain it will inaugurate a new era and a new relationship between the two countries.

After an overnight stay in Mexico, President Obama departs for Trinidad and Tobago Friday to attend the Summit of the Americas.