BANGKOK, Thailand - Suspects arrested in Spain and Thailand in connection with an international ring that provided forged passports to terrorists may have passed fake documents to the perpetrators of the 2004 Madrid bombings, Thai authorities said Thursday.

The arrests of seven people in Spain and three in Thailand this week represent a major achievement in dismantling one of the world's most notorious forgery rings -- one known for its skill in providing fake documents to criminal and terror enterprises -- said Jaime Fa, a police attache at the Spanish Embassy in Bangkok.

At a press conference in Bangkok, Thai Pol. Col. Naratch Sawetanant of the Department of Special Investigation said Spanish police have evidence that some of the suspects arrested this week provided fake identification documents to the Muslim militants blamed in the bombing attack six years ago on Madrid's commuter trains. Some 191 people were killed and more than 1,800 wounded when 10-shrapnel filled bombs ripped through the Spanish capital's commuter trains during rush hour on March 11, 2004.

Muhammad Athar Butt, 39, and Zeeshan Ehsan Butt, 27, both of Pakistan; and Sirikanya Kitbamrung, 25, of Thailand were arrested at a checkpoint on Nov. 30 while trying to enter Laos. They face possible charges of allegedly receiving stolen passports from networks in Spain and elsewhere in Europe via regular mail and then altering the passports for clients, said Naratch.

Police found items used to produce fake documents such as passports, entry-exit stamps, and visa stickers during a raid of the trio's Bangkok apartment on Wednesday, Naratch said.

"The group supplies fake passports to many groups, including those involved in terrorism, credit card fraud, human trafficking, weapons trading and illegal immigration," Naratch said.

The arrests in Spain took place late Tuesday and early Wednesday in the northeastern city of Barcelona. The detainees included six Pakistanis and one Nigerian. The Spanish Interior Ministry said the group stole passports, mostly from tourists in the Barcelona area, and sent them to Thailand to be doctored and later distributed to groups linked to al Qaeda.

The Spanish Foreign Ministry said Wednesday the suspects also had links to Lashkar-e-Taiba, a Pakistan-based terrorist group blamed for the 2008 Mumbai, India, attacks that killed 166 people. They also allegedly supplied forged documents to other groups, including the Tamil Tiger rebels who were crushed last year by Sri Lankan troops after a quarter-century war for an independent state for ethnic minority Tamils.