WASHINGTON — President Obama, speaking hours after a gunman killed a student and wounded a teacher at an Oregon high school, said Tuesday that his failure to push through stricter gun laws was the greatest frustration of his presidency, declaring, “We’re the only developed country on earth where this happens.”

Speaking in blunt and bitter terms about a bloody trail of shootings in the last month, Mr. Obama said: “Our levels of gun violence are off the charts. There’s no advanced, developed country on earth that would put up with this.”

While the president said he had undertaken several executive actions to tighten existing regulations, the failure to require a background check for buyers of guns left the nation vulnerable to an unending series of mass shootings. “The bottom line is, is that we don’t have enough tools right now to really make as big of a dent as we need to,” Mr. Obama said to a young audience at a White House question-and-answer session sponsored by the social media site Tumblr.

The string of shootings continued on Tuesday when a gunman at Reynolds High School in Troutdale, Ore., killed a 14-year-old student and wounded a physical education teacher. The authorities in Troutdale, a Portland suburb, did not immediately identify the gunman, who was armed with a rifle and later found dead at the scene. It was unclear if he was a student or knew either of the victims.