WASHINGTON, Dec. 4-- U.S. President Barack Obama on Wednesday called on Congress to raise the national minimum wage and reduce income inequality in the world's largest economy, in an effort to shift public focus away from the glitch-filled rollout of the Affordable Care Act (ACA).

Speaking during an event hosted by the Washington-based think tank the Center for American Progress, Obama said income inequality is the "defining challenge" for the United States, while a growing middle class is the engine of U.S. economic prosperity.

The rich Americans took a disproportionately large portion of wealth and the U.S. society is getting "profoundly unequal," Obama said as his Republican rivals ratcheted up assault on the ACA, commonly known as Obamacare.

"The top 10 percent no longer takes in one-third of our income - - it now takes half. Whereas in the past, the average CEO made about 20 to 30 times the income of the average worker, today's CEO now makes 273 times more," Obama added.

"The combined trends of increased inequality and decreasing mobility pose a fundamental threat to the American Dream, our way of life, and what we stand for around the globe," he said.

"Technology made it easier for companies to do more with less, eliminating certain job occupations. A more competitive world lets companies ship jobs anywhere. And as good manufacturing jobs automated or headed offshore, workers lost their leverage, jobs paid less and offered fewer benefits," he said.

The income inequality is hurting the country's middle class and the "opportunity gap" in the United States is growing, Obama said.

"A family in the top 1 percent has a net worth 288 times higher than the typical family, which is a record for this country," he said.

Obama used the opportunity to press Congress to raise the national minimum wage currently at 7.25 U.S. dollars per hour in a bid to help low-income workers and support economic growth.

"There's no solid evidence that a higher minimum wage costs jobs, and research shows it raises incomes for low-wage workers and boosts short-term economic growth," he added.

"As values of community broke down, and competitive pressure increased, businesses lobbied Washington to weaken unions and the value of the minimum wage. As a trickle-down ideology became more prominent, taxes were slashed for the wealthiest, while investments in things that make us all richer, like schools and infrastructure, were allowed to wither," Obama said.

Obama has repeatedly proposed an increase of national minimum wage, which is opposed by top Republican lawmakers.