By Kevin Liptak, CNN
(CNN) - New York City Mayor Michael Bloomberg, an outspoken advocate of stricter gun-control laws, said in a radio interview Friday the two candidates for president needed to take a firmer line in addressing gun violence.
Bloomberg's comments came as police and the FBI were investigating a deadly shooting in Colorado that left at least 12 people dead.
"Soothing words are nice, but maybe it's time that the two people who want to be president of the United States stand up and tell us what they are going to do about it, because this is obviously a problem across the country," Bloomberg said on WOR Radio's "The John Gambling Show."
Bloomberg continued, saying Friday's tragedy should spark greater focus on how guns reach killers.
"I mean, there are so many murders with guns every day, it's just got to stop," Bloomberg said. "And instead of the two people - President Obama and Governor Romney - talking in broad things about they want to make the world a better place, okay, tell us how."
"In the end, it is really the leadership at a national level, which is whoever is going to be president of the United States starting next January 1st - what are they going to do about guns?" Bloomberg asked.
Presumptive GOP nominee Mitt Romney met with Bloomberg in May, but an aide to the mayor said Bloomberg remained undecided about making an endorsement in the presidential race. Bloomberg won his last election as a political independent, but was previously a Democrat, then a Republican.
In his interview Friday, Bloomberg said guns getting into hands of criminals wasn't solely a problem in cities like New York.
"This is killing people every day, and it's growing and it's not just an inner-city, east coast, west coast, big city phenomenon. Aurora is not a big city," Bloomberg said, referring to the suburb of Denver where Friday's shooting took place.