The Islamist Wasat party condemned the arrest on Monday of its leader Abu al-Ila Madhi and his deputy Essam Sultan, Egyptian news website Ahram reported.
Wasat said the two men had committed no crimes, MSN Arabia reported.
The two men were arrested in Cairo’s Mokattam suburb, and transferred to Tora prison on the outskirts of the capital, where former President Hosni Mubarak and his two sons are also held.
The arrests “mark a return to an age we thought would never come back,” Wasat said in a statement.
The arrests of its leaders, supporters of ousted President Mohammad Mursi, follows the detention of several leading Islamist figures.
Mursi is himself under arrest, his whereabouts unknown.
Wasat was founded in the late 1990s by defectors from Mursi’s Muslim Brotherhood.
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