MEXICO CITY (AP) âÄî Confronting a Mexican drug war that is “sowing chaos in our communities,” President Barack Obama signaled Thursday he will not seek the reinstatement of a U.S. assault weapons ban but instead step up enforcement of existing laws banning the transfer of such guns across the border. Obama had pledged during his campaign to seek renewal of the ban but has bowed to the reality that such a move would be unpopular in politically key U.S. states and among Republicans as well as some conservative Democrats. Obama met here with Mexican President Felipe Calderon, who has been conducting an aggressive fight against drug cartels and had hoped to persuade Obama to push for reinstatement. Allies in the fight against drug cartels, Obama and Calderon took different stands on U.S. sanctions against Cuba. Calderon said the decades-long U.S. embargo has not been successful in forcing Cuba to adopt democratic reforms. “We do not believe that the embargo or the isolation of Cuba is a good measure for things to change,” the Mexican president said. Obama pointed to the announcement this week that the U.S. was softening sanctions, allowing Americans to make unlimited transfers of money and visits to relatives in Cuba. But he said Cuba needs to reciprocate with actions that are “grounded in respect for human rights.”