CAIRO—In the latest sign of the widening dissent within Egypt's Muslim Brotherhood, youth members of the country's most powerful Islamist group said they would start their own secular political party.

The announcement of the new party's founding on Tuesday came after the Muslim Brotherhood leadership expelled prominent reformist leader Abdel Moneim Aboul Fotouh on Saturday. Dr. Aboul Fotouh advanced himself in May as a candidate in presidential elections scheduled for this fall, violating the Brotherhood's pledge not to field a candidate.

Both the expulsion of Dr. Aboul Fotouh and the founding of Al Tayar Al Masry, or the Egyptian Current Party, point to growing dissatisfaction by Brotherhood moderates at what they say is a reluctance by Brotherhood leaders to tolerate internal dissent and embrace the country's shift toward democracy. While the new party is unlikely to approach the formidable political presence of the Brotherhood, such breakaway elements could damage the image of relative political inclusiveness the group long enjoyed as the most powerful opposition to the past regime.

Even after Brotherhood youth helped oust former President Hosni Mubarak in a nearly three-week uprising in February, the 83-year-old organization has continued to operate as it always has, with what dissident members call a domineering, top-down leadership structure.

"The problem is that a lot of the members of the Brotherhood have grown up under specific circumstances that are not like the circumstances of relative freedom" we have now, said Mohamed Aql, one of the young Brotherhood members who founded Al Tayar Al Masry. "Those leaders cannot understand the current environment we're living in right now after Mubarak."