Hillary Clinton said the Syrian National Council could "no longer be viewed as the visible leader of the opposition."
The Obama administration has said it would push for a major shake-up in Syria's opposition leadership, dismissing the Syrian National Council.
The US wants the opposition to rally wider support and resist attempts by extremists to hijack the revolution against the Assad regime.
Speaking to reporters in Croatia's capital, US Secretary of State Hillary Rodham Clinton said the administration was suggesting names and organisations that should feature prominently in any new rebel leadership that emerges from talks starting next week in Doha, the capital of Qatar.
She dismissed the Syrian National Council, a Paris-based group of regime opponents who have lived in exile for decades, saying its leadership days are over, even if it could still play a role. The council was viewed with suspicion by rebels who stayed in Syria and fought the regime of President Bashar al-Assad.
"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. "There has to be a representation of those who are on the front lines fighting and dying today to obtain their freedom. And there needs to be an opposition leadership structure that is dedicated to representing and protecting all Syrians."
