A newly formed Council of the Front of National Salvation, composed mostly of known Romanian dissidents and the army's chief of staff, announced on Radio Bucharest shortly before midnight that it had taken over until free elections can be held next April.
Pictures broadcast by Romanian television, which had been taken over by anti-Ceausescu forces earlier Friday, showed what appeared to be thousands of civilians apparently trapped in the crossfire as rival security units battled in the center of the city. Soviet television reported "hundreds dead in the streets."
Television also aired footage that showed residents in the western city of Timisoara digging up three mass graves where thousands of victims of last weekend's crackdown are believed to be buried.
In Bucharest, the lavish presidential palace, from which the 71-year-old dictator and his wife, Elena, had ruled like medieval potentates for 24 years before they fled by helicopter at about noon Friday, was ablaze, as was part of the Communist Party headquarters building.
Ceausescu's whereabouts was still a mystery after conflicting reports by the newly liberated Romanian media, which were monitored in the West.
Romanian television reported that he and Elena, who was also his second in command, had left the country for an undetermined destination. But Radio Bucharest, which was also in the opposition's hands, reported at various times that he had been captured, escaped, then captured again.
The station also reported late Friday that some of the pro-regime forces had surrendered, and the fighting was dying down. But other die-hards were said to be moving through secret tunnels beneath the city, and pockets of resistance remained.
Early today, Bucharest Radio reported that the head of the dreaded Securitate secret security force, which has remained loyal to Ceausescu, switched allegiance and ordered his forces to give up their arms and back the revolt.
The report, monitored in Vienna, said that Gen. Iulien Vlad was "with the people" and "orders all security troops to ally themselves with the army and the people."
It also said that Interior Minister Tudor Postelnicu and First Deputy Prime Minister Ion Dinca, a Politburo member and one of Ceausescu's most trusted men, had been arrested.
There were reports, too, of fighting in other cities, including Timisoara, the western provincial city where the anti-Ceausescu protests began last weekend.
A Bucharest-based British diplomat, in a live telephone interview broadcast by Independent Television News, appealed for Western relief agencies to send emergency medical supplies.
State radio broadcast repeated appeals for Romanians to detain the fleeing dictator, alerting listeners near dusk that he was headed toward Pitesti, northwest of Bucharest, in a red jeep with a broken front window--license plate number ARO244.
The official Soviet news agency Tass said he had used at least two automobiles as well as the helicopter in his attempted escape.
Ceausescu's son, Nicu, said to be a leader of Friday's counterattack by pro-regime security forces, was captured by protesters and shown on national television.
Romanian TV and the state news agency Agerpres said the younger Ceausescu had been captured after trying to assume command of the security forces in Sibiu, where there had been reports of fierce fighting between security forces and rebellious troops.
His face showed signs of bruising around the left eye, but he appeared in far better shape than two badly beaten students introduced earlier to underline the viciousness of the regime's death throes.