U.S. Secretary of State Hillary Clinton has called on African nations to cut ties with Libyan leader Moammar Gadhafi and give backing to Libyan rebels.

Clinton made the remarks Monday in a speech at African Union headquarters in Ethiopia's capital, Addis Ababa.

She urged African leaders to demand that Mr. Gadhafi accept a cease-fire with Libyan rebels and give up power. Clinton also called on them to expel pro-Gadhafi diplomats from their countries and support the Libyan rebel Transitional National Council.

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

Clinton cut short her visit to Ethiopia on Monday because of fears that an ash cloud from a volcano in Eritrea could affect her travel plans.

U.S. officials said Ethiopian officials planned to close the airport in Addis Ababa.

Clinton had planned to returned to the United States on Tuesday, after meeting with Ethiopian Prime Minister Meles Zenawi and visits to several places in Addis Ababa.

Ethiopia is the final stop on Clinton's four-nation trip. The trip began last week in the United Arab Emirates, where Italy, France, and other nations pledged $1.1 billion to help the Libyan rebels.

The secretary of state also visited Zambia and Tanzania.