President Mengistu Haile Mariam, the Marxist president who ruled Ethiopia through war and famine since 1977, resigned Tuesday under pressure from advancing rebels and left the country, state radio said.

The announcement came less than a week before peace talks are to begin, but rebel leaders reacted to Mengistu's departure with skepticism and vowed to continue fighting.In a noon broadcast, state radio said Lt. Gen. Tesfaye Gebre-Kidan had taken over administration of this impoverished nation of 51 million people. It quoted the Council of State, a group of Mengistu advisers.

The council said steps had been taken to "arrange a cease-fire through diplomatic channels" and the U.S. Embassy in Addis Ababa confirmed that it had immediately contacted the rebels.

Mengistu's destination was not announced. Reliable sources said they believed he had arrived in Nairobi, in neighboring Kenya, but that could not immediately be confirmed. Other sources said he may have fled to Zimbabwe.

The Bush administration welcomed Mengistu's resignation and departure. White House spokesman Roman Popadiuk called on government and insurgent forces to cease operations, saying the United States hopes "the door is open for the realization of peace and democracy in this tragic situation."

The departure of Mengistu, 49, follows three months of dramatic rebel gains in the north and west. Heavy fighting raged Tuesday for a sixth straight day north and west of the capital, with insurgents moving to within 40 miles of the capital, Addis Ababa.

The rebels have said they have no intention of trying to march on the capital.

A Tigrean rebel spokesman described Tesfaye, the general now in charge, as having been Mengistu's right-hand man and responsible for government military strategy.

The spokesman, Asefa Mamo, said Mengistu's departure simply removed "one evil person" and didn't significantly change the government.

"Until things are clarified we will go on fighting," said Giorgis Petrosia, a spokesman for the other main rebel group, the Eritreans.