Rebels said Thursday they had fought to within about 20 miles of the capital, and the government deployed tanks and hundreds of soldiers to protect the presidential palace.

Diplomats continued to try to halt the fighting and persuade the two main rebel groups, the Eritreans and Tigreans, to attend U.S.-mediated peace talks set for Monday in London.The rebels have rejected a ceasefire call by Lt. Gen. Tesfaye Gebre-Kidan. He took over the government on Tuesday when Mengistu Haile Mariam resigned after 17 years of repressive rule and fled to Zimbabwe.

Tanks and hundreds of soldiers took up positions Thursday at the sprawling grounds of the old presidential palace on the city's north side.

Five tanks were seen guarding its three entrances, and soldiers were spaced only a few feet apart inside the heavy fence surrounding the compound.

However, similar defensive preparations could not be seen at the Foreign Ministry, the Ministry of Information, which houses the national radio station, the television station or other key government buildings.

The acting government, seeking to placate its foes, said Thursday it freed 171 political prisoners, most of whom were arrested after a coup attempt in 1989.

Officials also began removing reminders of the country's Marxist past, but it was doubtful the rebels would be impressed with the moves.