Madrid ( CNN ) -- Spanish police arrested eight suspected Islamic militants in Madrid in predawn raids Monday , for allegedly recruiting and sending radical fighters to aid the terrorist group Islamic State in Iraq and Syria , the Interior Ministry said in a statement . The arrests come just ahead of the proclamation of Spain 's new King Felipe VI on Thursday in parliament , and the ministry last week raised the terror alert level from 2 to 3 , to tighten security in the capital during the festivities . The suspected leader of the cell broken up Monday had been detained in Afghanistan in 2001 and later was a prisoner at the U.S. base at Guantanamo Bay , Cuba , the ministry said . Just last month , police arrested six Spanish men in the Spanish enclave of Melilla , on Morocco 's north coast , on suspicion of recruiting and sending 26 radical Islamic fighters for terrorist groups in Syria , Mali and Libya . Also in Melilla , last March , a Spaniard and two Frenchmen were arrested on similar charges . The movement of Islamic militants from Europe and North Africa to conflict zones such as Syria , Mali and Libya -- and their eventual return to Spain to potentially carry out terrorist attacks -- has been a prime concern for authorities battling terrorism . This week , thousands of police and security forces will be on alert throughout Madrid ; King Juan Carlos , 76 , Spain 's head of state and commander in chief , formalizes his abdication Wednesday , leading to the proclamation of his son , Crown Prince Felipe , 46 , as the new King , in a nation where the elected government runs the country . The new King and his wife , Princess Letizia , who will become queen of Spain , are due to ride through the streets , from Parliament to the royal palace , and city officials have urged Spaniards to turn out for the parade and to hang Spanish flags from their homes .
They 're thinking of recruiting , sending fighters to aid the ISIS terrorist group . The cell 's suspected leader had been a prisoner at Guantanamo Bay , Cuba , ministry said . The arrests came just ahead of the proclamation of Spain 's new King Felipe VI on Thursday . This week , thousands of police and security forces will be on alert during coronation festivities .