Mohamed ElBaradei, the former head of the U.N. nuclear watchdog turned Egyptian reform campaigner, arrived in Cairo on Thursday after saying it was time for President Hosni Mubarak to quit and that he was ready to "lead the transition" in Egypt if asked.

ElBaradei, 68, arrived from Vienna, where he lives, to join a growing wave of protests against Mubarak inspired by Tunisia's overthrow of their authoritarian president.

"It is a critical time in the life of Egypt. I have come to participate with the Egyptian people," said ElBaradei as he left Cairo airport, where he was greeted by a small group of supporters.