These included the 2004 Madrid bombings, when blasts on packed commuter trains in a city suburb killed 191 people and wounded 1,841 others.
However, Spanish authorities have not confirmed any such link to those arrested.
The seven -- six Pakistanis and a Nigerian -- were held in raids in Barcelona on Tuesday night.
Three others -- two Pakistanis and a Thai woman -- were held in Thailand as part of the same Operation Kampai.
The judge in Madrid's National Court, which handles terrorism cases, ordered Junaid Humayun and Atiqur Rehman, both Pakistanis, and Nigerian Babatunde Agunbiade held without bail on suspicion of "collaborating or belonging to a terrorist organisation," the sources said.
Another Pakistani, Jabran Asghar, was freed on 10,000 euros (13,000 dollars) bail, three others were released on condition they do not leave Spain and appear at a police station every two weeks, and one, Mohammad Saddique Khan Begum, was freed unconditionally.
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