ZAGREB, Croatia — The Obama administration renounced the proclaimed leaders of the Syrian political opposition on Wednesday and said any group seeking to oust President Bashar Assad must reject attempts by extremists to hijack a legitimate revolution.
Secretary of State Hillary Rodham Clinton said the Syrian National Council should no longer be considered the ‘‘visible leader’’ of the opposition. That made official what has been the increasingly obvious sidelining of an opposition group led mostly by middle-age Syrian expatriates.
‘‘This cannot be an opposition represented by people who have many good attributes but have in many instances not been inside Syria for 20, 30, or 40 years,’’ Clinton said during a five-nation Balkans tour. ‘‘There has to be a representation of those who are on the front lines fighting and dying today.’’
The United States has no direct power to anoint the would-be new leaders of Syria, but US backing will be essential for any hopefuls seeking outside financial, diplomatic, or possible military assistance.
The United States is supporting new opposition leaders who will attend a strategy session in Qatar next week, Clinton said.
‘There has to bea representation of those who are on the front lines fighting and dying today.’
Clinton and other US officials are fed up with infighting among the Syrian National Council leaders seeking recognition as a shadow government and have become convinced that the group does not represent the interests of all ethnic and religious groups in Syria.
It also has little legitimacy among activists and fighters on the ground, and has done little to stem the infiltration of Islamist extremists into the opposition forces.
Clinton had some of her strongest words to date about the risk that the uprising against Assad could be overtaken by militants who do not seek a democratic replacement.
‘‘We also need an opposition that will be on record strongly resisting the efforts by extremists to hijack the Syrian revolution,’’ Clinton said.
The United States and other Western and Arab nations have called on Assad to step down. Russia, China, and Iran continue to back him.
The Obama administration’s shift away from the Syrian National Council comes as an internationally sanctioned truce failed to take hold. More than 500 people were killed during what was supposed to be a four-day cease-fire ending Monday.
Clinton said she was saddened but not surprised and made clear the United States is not betting on UN-sponsored diplomacy to end the fighting.
She said nothing about possible military intervention, something the United States has opposed as unworkable and counterproductive. Some Syrian activists hope that calculation will change after the US presidential election.
The State Department helped to smuggle a few internal dissidents out of Syria and brought them to New York last month to meet with representatives of key nations trying to help the opposition, Clinton said.
Also Wednesday, Turkish Prime Minister Recep Tayyip Erdogan said it is up to the UN Security Council to decide whether a no-fly zone should be imposed on Syria or safe areas created for civilians fleeing the civil war.