U.S. Secretary of State Hillary Clinton has called on African nations to cut ties with Libyan leader Moammar Gadhafi and demand his removal.

Clinton made the call in a speech Monday at the African Union headquarters in Addis Ababa, before cutting short her African tour over concerns about an ash cloud from an erupting volcano in nearby Eritrea.

She told the African leaders gathered in the Ethiopian capital that Mr. Gadhafi has lost his legitimacy to rule. Clinton urged them to call for a genuine cease-fire and throw their support behind the Libyan rebel's Transitional National Council.

She also called for the expulsion of Libyan diplomats from AU member countries.

Shortly after her speech, Clinton abruptly left Ethiopia and flew back to Washington as the ash cloud began disrupting air operations in the region.

Clinton is the first U.S. secretary of state to address the 53-member AU.

She warned that if Mr. Gadhafi remains in power, thousands of refugees will continue to flow out of Libya, and regional instability will grow worse with Libya's neighbors bearing the consequences.

The secretary had originally planned to remain in Addis Ababa until Tuesday to confer with the Ethiopian prime minister, Meles Zenawi and visit several projects designed to empower women.