Clinton, the first U.S. secretary of state to address the 53-member Africa
n Union, said unreformed African leaders were themselves at risk from the same tide of democracy sweeping the Middle East, proclaiming "the status quo is broken and the old ways of governing are no longer acceptable."
"It is true that Gaddafi has played a major role in providing financial support for many African nations and institutions, including the AU," Clinton said in her speech at the AU's headquarters in Ethiopia's capital, Addis Ababa.
"But it has become clear that we are long past the time when he can remain in power."
Clinton urged African states -- many with long-standing diplomatic and financial ties to the oil-rich Libya
n leader -- to join the international coalition demanding his exit as the condition for a ceasefire.
She also urged them to close pro-Gaddafi Libyan embassies, expel his diplomats and build ties with the Benghazi-based rebel National Transitional Council, which the United States and its European and Arab allies are promoting as a future interim government for the country.
Shortly after Clinton's AU speech, aides said her pilots had advised that an approaching ash cloud risked stranding her in the Horn of Africa if she did not depart swiftly.
Eritrea's long-dormant Dubbi volcano erupted at around midnight on Sunday after a series of earthquakes in the remote, arid region bordering Ethiopia, hurling a plume of ash 13.5 km into the sky, the France-based Volcanic Ash Advisory Center said.
U.S. officials said the ash cloud was headed toward Addis Ababa.
"CHASED BY A VOLCANO"
Clinton met Ethiopian Prime Minister Meles Zenawi as planned but canceled a scheduled media briefing to make time for meetings with delegations from Sudan's north and south.
Violence is worsening in parts of Sudan ahead of the south's formal independence on July 9. Sudanese President Omar Hassan al-Bashir agreed on Sunday to pull troops out of the disputed border region of Abyei before the south secedes -- a move which could help reduce tension.
However, the two sides have yet to agree on sensitive issues such as where to draw the common border and how to share oil revenues, leaving the potential for further conflict.
Clinton, speaking before her arrival in Addis Ababa during a stop in Tanzania, said the United States supported a proposal to put Ethiopian peacekeepers in the disputed Abyei region.
"I was hoping to spend a long time talking to you but I am being chased by a volcano," Clinton told south Sudan's President Salva Kiir.
She had a separate meeting with Nafie Ali Nafie, one of Bashir's main advisers. There were no immediate details.
Clinton used her three-nation Africa tour to highlight the Obama administration's drive to increase trade ties with Africa and encourage better political and economic governance.
She praised many African countries for implementing reforms and moving away from a tradition of strongman rule. But on a continent where autocrats still rule from Equatorial Guinea to Zimbabwe, Clinton said more needed to be done.
"We know that too many people in Africa live under long-standing rulers -- men who care too much about the longevity of their reign and too little about the legacy that should be built for their country's future," she said.
U.S. officials say the African Union has played a constructive role in regional affairs like the political deadlock in Ivory Coast and mustering peacekeepers for other regional crises.
But the AU -- long the beneficiary of Gaddafi's largesse -- has declined to join calls for Gaddafi's removal, instead accusing Western nations of undermining its own efforts to find a solution to the conflict.