During a joint news conference at the White House, Obama praised Calderon for his “extraordinary courage” in fighting the violent drug gangs that have been responsible for deaths on both sides of the border. Obama pledged to speed up US aid to train and equip Mexican forces to help in those efforts, but he also acknowledged that the United States must stem the flow of cash and guns to Mexico that have aided the drug runners.

“We are very mindful that the battle President Calderon is fighting inside of Mexico is not just his battle; it’s also ours,” Obama said. “We have to take responsibility, just as he’s taken responsibility.” Calderon’s visit comes three weeks after US Immigration and Customs Enforcement agent Jaime Zapata was shot to death in northern Mexico with a gun smuggled in from the US The incident raised questions in the US about Mexico’s ability to control violence and has Obama administration officials considering arming US agents working across the border to ensure their safety.

Mexican law forbids foreign law enforcement agents working in the country to bear arms, and Calderon vehemently expressed his opposition to making an exception for US personnel. But he said Zapata’s death showed a need to consider alternative methods for protecting agents.

“His death must urge us to work together to ensure a prosperous and peaceful future for our region,” Calderon said.

Obama said the US is seeking extradition of several suspects arrested in Mexico in connection with Zapata’s death.

Tensions between the North American allies were already heightened ahead of Zapata’s death. Secret State Department cables released last year revealed a grim assessment by US officials of Mexico’s ability to fight drug cartels, saying the country has limited intelligence-gathering capacity and quoting Calderon as saying politicians could be tempted to return to a tacit policy of tolerating the gangs.

In a show of confidence in Calderon’s efforts, the Obama administration said it would continue to send aid to support Mexico in the drug war. A senior administration official said the US plans to speed up implementation of the $1.4 billion Merida Initiative, with $900 million to be doled out by the end of the year. The official, who spoke on the condition of anonymity, was not authorized to speak publicly about the agreement.

Stephen Johnson, director of the Americas Program at the Center for Strategic and International Studies, said that given the breadth of the U.S-Mexico relationship, it was critical that Obama and Calderon meet before tensions escalated further.

“There are junctures like this where leaders have to get together and work through any misunderstanding that there might be, and then agree ways on ways to move forward,” Johnson said.

Eager to show signs of a productive partnership, Obama and Calderon agreed to a phased-in plan that would authorize both Mexican and US long-haul carriers to engage in cross-border operations provided the Mexican trucks meet US safety standards. Both countries were given this authority under the 1994 North American Free Trade Agreement, but the US has refused to allow Mexican trucks access amid concerns over their ability to meet stringent US safety and environmental standards.

Mexico has placed higher tariffs on dozens of US

products in response to the unresolved dispute. Under the proposed agreement, Mexico will agree to lift those tariffs in phases, with all tariffs lifted once the first Mexican carrier receives authorization to travel on US roads.

Negotiating teams, which are still working out details of the plan, are expected to send an agreement to Congress this spring.

News of a pending agreement won Obama praise from some in the business community, who have argued that the delay in opening cross-border trucking and the resulting tariffs have cost Americans jobs.

Tom Donohue, president of the US Chamber of Commerce, said completing a deal between the United States and Mexico would be, “a major step toward providing certainty to trucking companies and shippers throughout North America.” Johnson said it was important for the US and Mexico to lower tensions ahead of Obama’s trip to Latin America this month. He will visit Brazil, Chile and El Salvador.

Calderon last visited the White House in May, at the height of the debate over Arizona’s immigration law that makes it a crime to be in the United States illegally and requires police to question people about their immigration status if there is reason to suspect they are in the country illegally. Mexican officials strongly oppose the law, as does Obama, who told Calderon on Thursday that he still is committed to comprehensive immigration reform. It is vital to the US economy, he said.