NEW : Obama says plan seeks to halt terrorists from entering Mexico from U.S . Homeland Security chief says he wants to prevent ` ` spillover violence '' in U.S. More federal agents , equipment and personnel to be moved to Mexican border . Gun control advocacy group says Mexican drug gangs exploit weak U.S. gun laws .
NEW : Obama says plan seeks to halt weapons from entering Mexico from U.S . Homeland security chief says plan tries to prevent `` spillover violence '' in U.S. More federal agents , equipment and resources to be moved to Mexican border . Gun control advocacy group says Mexican drug gangs exploit weak U.S. gun laws .