Pressure from the Mexican government to stop cross-border gun purchases by drug cartels is giving some lawmakers hope for a compromise on gun control.

In a joint White House press conference with Mexican President Felipe Calderon today, President Obama spoke of shared responsibility on security measures to stop the cartels from buying guns in the U.S. Approximately 90 percent of the guns seized from cartels from fiscal 2006-2008 were purchased in the United States, according to a Government Accountability Office report released last year. The only place Mexicans can buy a gun legally is in an army-owned gun store in Mexico City.

Calderon has in the past year pressured Obama and other U.S. politicians to reinstate the assault weapons ban or ratchet up gun security. He has met with several lawmakers about gun trafficking, including Rep. Eliot Engel, D-N.Y., chairman of the House Foreign Affairs Subcommittee on the Western Hemisphere.

"I've met with Calderon about five times now," Engel said in an interview with NationalJournal.com last week. "... I hope we can get together and do something now to stop the cartels who buy guns in border states to go murder people."

Approximately 23,000 people have died from cartel-related violence throughout Mexico since Calderon took office in late 2006 and launched an offensive against the cartels, according to Mexican government figures. These figures do not include gang wars and other violence by cartel members operating in the United States.

Obama said today that he had directed the Department of Homeland Security and other agencies to "ramp up our efforts at interdicting" the money and guns that have kept the cartels heavily armed against more than three years of Calderon's counternarcotics campaigns.

Homeland Security Secretary Janet Napolitano has also focused on interdiction efforts recently, telling an audience at the Brookings Institution this month that "there's probably not much appetite in Congress for reinstituting the assault weapons ban."

Yet interdiction alone can't stop gun trafficking, said retired Col. Robert Killebrew, a senior fellow at the Center for a New American Security doing a study on Mexican and South American cartels. Killebrew said increased enforcement of existing gun control laws will help in tandem with a shutdown of international gun trafficking routes.

"If the cartels can't buy guns from the U.S., they will buy them somewhere else," said Killebrew, a Second Amendment rights advocate.

"Since the assault weapons ban expired in 2004, the seizures of fully automatic and semi-automatic weapons in Mexico have gone through the roof," said Mexico's ambassador to the U.S., Arturo Sarukhan. "What we are asking of the administration -- and of Congress -- is to enforce what is already on the books."

At the start of Obama's term, Engel and 52 other House members sent a letter to the president pressuring him to reinstate the assault weapons ban because it could be reinstated without writing a new law. While he's disappointed the administration has not indicated support for the ban, Engel observed last week that "there isn't much stomach in the Congress to do that."

"This is not about Second Amendment rights, this is about selling guns to people who go south of the border to murder and to wage war against the Mexican government," Engel said. "What I'm looking for is something that can be done right now that I think would have a great effect, like closing gun-show loopholes."

In addition to that loophole, which lets someone buy weapons from private sellers without a background check, cartels can buy guns via "straw purchases," made through citizens with clean records.

Closing the gun-show loophole to shut down trafficking is one avenue being explored by lawmakers, including New York Mayor Michael Bloomberg's Mayors Against Illegal Guns coalition. Another soft spot is the "terror gap" being targeted by Rep. Peter King, R-N.Y., who introduced a bill last year to restrict gun purchases by people who are suspected of terrorist links. According to the FBI, more than 1,100 legal purchases of weapons or explosives since 2004 were made by people on terror watch lists.

"We must do all we can to keep our cities and communities safe from terror and violence," King said May 5 when he spoke with Bloomberg and others before the Senate Committee on Homeland Security and Governmental Affairs.

Gil Kerlikowske, director of the Office of National Drug Control Policy, also raised the cartels as a global security concern in an interview with NationalJournal.com on May 4. "There's a significant shift from the Caribbean onto West Africa and Europe, and that's why the joint interdiction forces are so important," he said.

Killebrew says his study, due out in September, labels Mexico's cartels as "an international insurgency because they seek to threaten the power of government" and calls for a broader strategy to stop their access to guns.

"These guys are after quantities, so there could be more laws against buying in bulk, the way they have in Virginia," Killebrew said. "If you pitch this as a Second Amendment right, all progress will probably stop. But if you pitch it as a larger war against cartels, there is some compromise that could be made."