The Interior Ministry said Thursday the brothers were detained in Brussels on a European-wide warrant issued by Spain's National Court. It did not say when the arrests were made.
So far eight alleged members of the cell have been arrested in Barcelona and three in Thailand, where the group was allegedly based. Spain named the new detainees as Mudaser Butt, 32, and Naveed Shahzad Butt, 30.
Spain says the group sent stolen passports to Thailand to be doctored and distributed to groups linked to al-Qaida, mainly Lashkar-e-Taiba, a Pakistan-based terror group blamed for the 2008 Mumbai, India, attacks that killed 166 people.