MADRID, Spain — Hundreds of police and security officials arrested at least 11 suspected Islamic militants in pre-dawn raids yesterday in the Spanish African enclave of Ceuta, nabbing them at their homes and while they prayed in local mosques.

The men — including 10 Spaniards and one Moroccan — had recently begun discussing taking concrete action to launch an attack, though they were in the early stages and are not believed to have selected a target, Interior Minister Alfredo Perez Rubalcaba, who was traveling in Algeria, said.

“It was an Islamic cell in the process of being formed, so they had no specific targets,” Mr. Rubalcaba said. “But when we saw that they were moving from fanatic discussion to direct action, we moved ahead to detain them.”

Among those arrested by officials acting on months of intelligence were two brothers of a Spaniard detained at the American military prison at Guantanamo Bay, Cuba, until 2004, Hamed Abderrahman Ahmed, officials said. Mr. Ahmed himself was not taken into custody, police said.

Forces sent by boat from the Spanish mainland carried out the operations in neighborhoods all over the city, a police official in Ceuta told the Associated Press. A national police official said 300 security agents took part in the operation.