Spanish police said Thursday they had dismantled a ring suspected of financing Al-Qaeda and arrested three men, including the top representative of Spain's Muslim community.

Those detained were suspected of having "exploited an NGO to finance the activities of terrorist fighters," a National Police statement said.

The organisation is believed to have collected donations for orphaned children in Syria, but "a part" of the funds went instead to areas of Syria "controlled by Al-Qaeda militias with the aim of supporting their fighters", it added.

"Another part of the proceeds was destined to defray the expenses of a school centre for orphaned children located in a conflict zone, whose activities were focused on the training of future mujahideen."

The head of the Islamic Commission of Spain (CIE), Mohammad Ayman Adlbi, was arrested Tuesday as part of the operation and later released without charge, police and government sources said.

"I must express our confidence in the judicial administration, regardless of the suspicions, which we consider unfounded," Ayman Adlbi said in a statement released late Wednesday by the CIE. He also voiced his "great displeasure" at being arrested when he could have easily been invited for "an interview" at the police station. 

Ayman Adlbi was appointed last year to head the CIE, which represents Muslims before Spanish state bodies and oversees religious services at the country's mosques as well as Muslim education.

One of the men arrested, a treasurer of a federation which is part of the CIE, the Union of Islamic Communities of Spain, was placed in preventative detention, a judicial source said.

Police said the arrests follow a two-year investigation.

Since 2015, Spain's alert level has been held at level four out of five, indicating a high risk of an attack.