Washington, Dec 5 (IANS): President Barack Obama Wednesday said income inequality is the "defining challenge" for the US while a growing middle class is the engine of the country's economic prosperity.

Speaking during an event hosted by the Washington-based think tank the Center for American Progress, Obama said the rich Americans took a disproportionately large portion of wealth and the US society was getting increasingly unequal, Xinhua reported.

The challenge is posing a "profound" threat to the American Dream and it is an issue that Washington should tackle seriously, he said.

The income inequality is hurting the country's middle class and the "opportunity gap" in the US is growing, he said, adding that the world's largest economy needs a growth strategy.

Obama also used the opportunity to press Congress to raise the national minimum wage currently at $7.25 per hour in an effort to help low-wage workers and boost economic growth.