Echoing themes of civil rights and social justice, President Barack Obama said Saturday that until the U.S. becomes a place where anyone who is willing to work hard can earn a way into the middle class "we can't let up and we can't rest."

"We can't rest until we offer new ladders of opportunity for anyone willing to climb them," Obama said in a keynote address to the Congressional Black Caucus Foundation's annual awards dinner. "Over the last 30 years, upward mobility in this country - the idea that if you work hard, you can get ahead - has slipped out of reach for too many Americans. And that's especially true in communities with large African-American populations."

Obama hewed to the theme of the dinner, which this year celebrated the "Spirit of 1963," including the civil rights movement and the March on Washington for Jobs and Justice led 50 years ago at the Lincoln Memorial by Martin Luther King Jr., and the advances it brought about for black Americans. Topping the list of achievements is Obama's election in 2008 as America's first black president.

Without mentioning his place in history, Obama acknowledged progress made since 1963, but said there was more to be done. He spoke of work needed to reduce a black unemployment rate that is twice that of whites, increase the minimum wage and provide health care and education for all.

"We must make this country a place where anyone who works hard can earn their way into the middle class," Obama told hundreds of his most ardent supporters packed into a cavernous ballroom at Washington's convention center. "And until we do, we can't let up and we can't rest."

Obama also sounded a note of caution about recent mass shootings, including at the Navy Yard in Washington last Monday where authorities say 12 people were slain by a gunman who later was killed by police. Two days ago in Obama's hometown of Chicago, 13 people were shot during a game of pickup basketball, including a 3-year-old girl.

Obama lamented the failure earlier this year to get gun legislation through the Senate and said "that means we've got to get back up and go back at it" to work harder than those he said want to make it easier for people to get firearms.

"We've got to work as hard as possible for the sake of our children," he said.

Obama is scheduled to speak Sunday at a memorial service for victims of the Washington shooting.