"None of us really have influence other than say what we believe and to encourage the changes that we hope for ... We don't know how this is gonna end yet,"US Secretary of State Hillary Clinton, on a two-day visit to Turkey, Syria's northern neighbour, said on CNN Turk television on Saturday.
"What's happening in Syria is very uncertain and troubling because many of us had hoped that president (Bashar) Assad would make the reforms that were necessary," she said.
Clinton spoke in Istanbul as some 350 Syrian dissidents gathered in the city to discuss strategies to unseat Assad's regime, a day after activists said at least 28 civilians were killed in a clampdown on the largest anti-regime rallies in Syria in four months.
"The brutality has to stop. There must be a legitimate sincere effort with the opposition to try to make changes. I don't know whether that will happen or not," Clinton said, without any direct comment on the opposition gathering.
The Syrian turmoil was expected to be on Clinton's agenda in meetings with Turkish leaders later Saturday.
Ankara, whose ties with Damascus have flourished in recent years, has piled pressure on Assad to initiate reform, while stopping short of calling for his departure.
However Turkish frustration with his foot-dragging on reform has grown.
Speaking at a meeting of the Libya contact group in Istanbul Friday, Clinton said that "Syria can't go back to the way it was before" after the anti-regime protests broke out in March.
Assad "has lost his legitimacy in the eyes of his own people because of the brutality of their crackdown," she said.
Four European countries -- Britain, France, Germany, Portugal -- have for several weeks been drafting a resolution to put before the UN Security Council, condemning the crackdown and calling for political reforms.
But China and Russia -- the latter a longtime strategic ally of Syria -- maintain their opposition to any international interference in the country.