110 people were briefly detained and 10 injured during a protest on Monday in support of a prominent Muslim Brotherhood member who was on trial in Zagazig in northern Egypt, a member of the organization said.
"Thousands of riot police surrounded a demonstration by 2,000 members of the Brotherhood in support of Dr Hassan al-Hayawan," the group's website reported.
"The security forces treated the protesters harshly, using tear gas and rubber bullets and truncheons, which led to the injury of at least 10 members," it said.
Egypt's interior ministry was not immediately available for comment.
Hayawan, who was charged with the illegal possession of weapons and belonging to an illegal organisation, was acquitted by the Zagazig state security emergency court.
The officially banned organisation fielded candidates as independents in the November-December parliamentary elections and won 20% of seats in the People's Assembly, becoming the country's largest opposition group.
In recent weeks, hundreds of members of the group have been detained after joining demonstrations in support of judges calling for independence from the executive.
The arrests come shortly after the US Congress narrowly voted not to cut aid to Cairo, a move intended to show US displeasure with Egypt's democratic situation. Egypt is the second largest recipient of US aid after Israel.
The United States publicly criticised Egypt three times last month for its harsh crackdown on political dissent.