WASHINGTON — President Obama declared Syria’s main opposition group the sole “legitimate representative” of its country’s people Tuesday, deeming the move “a big step” in the international diplomatic efforts to end Syrian President Bashar Assad’s embattled regime.

Obama said the newly formed Syrian Opposition Council “is now inclusive enough” to be granted the elevated status, which paves the way for the greater U.S. support for the organization.

“Obviously, with that recognition comes responsibilities,” Obama said in an interview Tuesday with ABC News. “To make sure that they organize themselves effectively, that they are representative of all the parties, that they commit themselves to a political transition that respects women’s rights and minority rights.”

Recognition of the council as the sole representative of Syria’s diverse population brings the U.S. in line with Britain, France and several of America’s Arab allies, which took the same step shortly after the body was created at a meeting of opposition representatives in Qatar last month.

Obama’s announcement follows his administration’s blacklisting of a militant Syrian rebel group with links to al-Qaida. That step is aimed at blunting the influence of extremists amid fears that the regime may use or lose control of its stockpile of chemical weapons.

U.S. recognition of the opposition council is expected to be a centerpiece of an international conference on the Syria crisis in Morocco this week. Secretary of State Hillary Rodham Clinton had been due to attend Wednesday’s meeting in Marrakech but canceled her trip because she was ill with a stomach virus.