The Arab world's revolutions could end up "just a mirage in the desert" if leaders fail to make good on demands for greater democracy and economic opportunity, US secretary of state Hillary Clinton has said.
Her warning, delivered at the annual US-Islamic World Forum held in Washington, comes amid increased signs of a backslide in the so-called Arab Spring, as Libya's Muammar Gaddafi persists with a bloody war against rebels and leaders from Yemen to Syria to Bahrain violently resist calls for a democratic transformation.
In January she warned Arab governments that they risked "sinking into the sand" if they did not meet their people's needs. On Wednesday Mrs Clinton said upheaval in the Arab world presented the first real chance in decades for fundamental change in the region.
"Will the people and leaders of the Middle East and North Africa pursue a new, more inclusive approach to solving the region's persistent political, economic and social challenges?" she asked.
"Will they consolidate the progress of recent weeks and address long-denied aspirations for dignity and opportunity? Or, when we meet at this forum in one year or five years or 10, will we have seen the prospects for reform fade and remember this moment as just a mirage in the desert?"
The speech was in many ways a sequel to Mrs Clinton's January warning in Doha, Qatar. A day later, Tunisian president Zine El Abidine Ben Ali fled his country amid mass protests demanding his ousting. Egypt's Hosni Mubarak stepped down under similar pressure a month later.
Mrs Clinton did not answer the fundamental question she posed - whether the unrest would produce truly free societies with economic opportunities for their people, or leave corrupt and repressive systems in place.
She stressed that much had already been accomplished, with protest movements shattering the myth that Arabs did not share the same aspirations for freedom, dignity and opportunity, or that change could only come through violence.
She said Facebook, Twitter and other social media networks had helped mobilise younger citizens who were increasingly connected and unwilling to be silenced by tanks and missiles.
"Changing leaders alone will not be enough to satisfy them," Mrs Clinton said.