WASHINGTON — President Barack Obama on Sunday memorialized the victims of the Washington Navy Yard shooting by calling for a transformation in the nation’s gun laws to address an epidemic of gun violence, saying, “There’s nothing inevitable about it.”

Obama said Americans should honor the victims of last Monday’s mass shooting by insisting on a change in gun laws. “It ought to obsess us,” Obama said.

He said no other advanced nation endures the kind of gun violence seen in the United States, and blamed mass shootings on laws that fail “to keep guns out of the hands of criminals and dangerous people.”

“What’s different in America is it’s easy to get your hands on a gun,” he said. He acknowledged “the politics are difficult,” a lesson he learned after failing to get expanded background checks for gun buyers through the Democratic-controlled Senate this spring.

“And that’s sometimes where the resignation comes from: the sense that our politics are frozen and that nothing will change. Well, I cannot accept that,” Obama said. “By now, though, it should be clear that the change we need will not come from Washington, even when tragedy strikes Washington. Change will come the only way it ever has come, and that’s from the American people.”

Obama joined military leaders in eulogizing the 12 victims killed in last Monday’s shooting, speaking from the parade grounds at the Marine Barracks, a site personally selected by Thomas Jefferson because of its close marching distance to the Navy Yard.

The invitation-only crowd included around 4,000 mourners.

Authorities say their loved ones’ lives were taken Monday by shotgun-wielding Aaron Alexis, a 34-year-old former Navy reservist and information technology contractor who struggled with mental illness. Police killed Alexis in a gun battle.

The military leaders who spoke before Obama at Sunday’s memorial service, including Defense Secretary Chuck Hagel, Navy Secretary Ray Mabus and Adm. Jonathan Greenert, chief of naval operations, avoided any mention of gun control. But Washington Mayor Vincent Gray spoke forcefully for action.

The service ended with a bugler playing taps and singing of the Navy hymn after a reading of the names of the fallen, who ranged in age from 46 to 73 and included civilian employees and contractors.