"Engineer Akram Zoheiry ... died Wednesday morning," Abdel
Moneim Mahmud, an official in the Muslim Brotherhood media
department, said, giving no further details of his death.
Though the movement - founded in 1928 in Ismailiya, Egypt, by Hasan al-Banna - is officially banned, some of the Muslim Brotherhood's activities are tolerated by the Egyptian government.
Zoheiry was one of 54 people arrested on 16 May accused of having organised protests against Israel's assassinations of Shaikh Ahmad Yassin, founding leader of the Palestinian Islamic resisting movement Hamas, and his successor Abd Al-Aziz al-Rantisi.
Last week, the Egyptian Organisation for Human Rights issued a report charging that at least 15 Egyptians had died while in police custody between April 2003 and April 2004.
The organisation said it had "strong suspicions that the 15 deaths resulted from torture and abuse at Egyptian police stations".
The figure represented only a fraction of the problem, the statement said, referring to reports of hundreds of other cases of torture across the country.