U.S. President Barack Obama says drug-related violence in Mexico could have what he calls a “deteriorating effect” on U.S.-Mexican relations.

Mr. Obama spoke Monday after a White House summit with Mexican President Felipe Calderon and Canadian Prime Minister Stephen Harper. Mexico's war against drug gangs fighting for turf near the U.S. border was a major topic at the talks.

Mr. Obama said that when innocent families, including women and children, are gunned down in the streets, it is everybody's problem.

“Criminal gangs and narco traffickers pose a threat to each of our nations. And each of our nations has a responsibility to meet that threat.”

Mr. Obama said the United States has a responsibility to reduce the demand for drugs and to stop guns and cash from flowing across the border into Mexico.

President Calderon said Mexico cannot stop the violence without a halt to gun trafficking. He called on the United States to renew an assault weapons ban, saying the ban's expiration in 2004 coincided with the rise in drug-related violence in his country.

About 50,000 people have been killed since 2006, when President Calderon sent the army into northern Mexico to tackle the drug gangs.

The three North American leaders also talked about the economy and trade. They spoke about the need to strip away regulations that they say stifle trade.

Prime Minister Harper said Canada has no immediate plans to scrap visa requirements for Mexican visitors. He said that is the only tool Canada currently has to effectively deal with what he calls large-scale phony refugee claims.

Also Monday, a U.S. federal judge in San Diego, California sentenced former Mexican drug gang leader Benjamin Arellano Felix to 25 years in prison. The judge also fined him $100 million.

Felix led the notorious Arellano Felix Organization — one of Mexico's largest and most violent drug trafficking rings. Prosecutors say the gang was responsible for murder, chaos and suffering on both sides of the U.S.-Mexican border.

Mexico extradited Felix to the United States for trial last year.