CAIRO, Egypt (AP) -- Police arrested 21 members of Egypt's largest opposition group, the outlawed Muslim Brotherhood, on Sunday on the country's Mediterranean Sea coast, the group and a police official reported.

Authorities accused the members of planning the group's activities while in the town of Marsa Matrouh, some 430 kilometers (270 miles) northwest of the capital Cairo, said the official, speaking on condition of anonymity because he was not authorized to speak to the press.

The Brotherhood's official Web site said the individuals were vacationing when police raided their cottages at dawn, arresting them and seizing their belongings.

"The security forces found all books, so it's going to be another summer resort arrest with no reason or charge," Abdel Moneim Abdel Maksoud, the group's lawyer, told The Associated Press.

Sunday's arrests raised the number of Muslim Brotherhood members detained in recent months to more than 535. Authorities have increasingly cracked down on the group.

The Brotherhood, which has been banned since 1954, is Egypt's largest Islamic opposition group. Its lawmakers, who run as independents, currently hold 88 seats in the 454-member lower house of the parliament.