The top leadership body of Egypt's ruling party resigned Saturday, including the president's son, but the regime appeared to be digging in its heels, calculating that it can ride out street protests and keep President Hosni Mubarak in office.

Protesters rejected the concessions and vowed to keep up their campaign until Mubarak steps down, convinced that the regime intends to enact only superficial democratic reforms and keep its hold on power. Tens of thousands thronged Cairo's central Tahrir Square in a 12th day of protests, chanting "He will go! He will go!"

But the United States gave a strong endorsement to Mubarak's deputy Omar Suleiman's handling of the transition, warning that order was needed to prevent extremists from hijacking the process. "It's important to support the transition process announced by the Egyptian government actually headed by now-Vice President Omar Suleiman," Secretary of State Hillary Rodham Clinton said at an international security conference in Munich, Germany.

Frank Wisner, the retired American diplomat sent by President Barack Obama to Cairo this past week to tell Mubarak that the U.S. saw his rule coming to an end, said Mubarak had to keep a leadership role at least temporarily if the "fragile glimmerings" of progress were to take hold as quickly as needed.

Mubarak insists he will remain in his post until his term ends in the autumn after presidential elections in September. Washington has said the transition should bring greater democracy to ensure a free and fair vote. But protesters fear that without an immediate Mubarak exit and the pressure from the streets, the regime will emerge with its authoritarian monopoly largely intact.