The judge who approved the charges also said a Turkish engineer who worked in Gibraltar for years and was arrested in the same case had paid for Spanish paragliding lessons for the men.
The court named the Russians of Chechen descent as Eldar Magomedov and Mohamed Ankari Adamov and said in a statement there was evidence linking them with "belonging to or forming part of a terrorist organization." The terror group was not specified, but Spanish authorities previously said it was al-Qaida, and the Islamic network has many affiliates.
The two men were driven to the court in dark unmarked government cars under tight security Sunday morning, escorted by police officers wearing masks to hide their identities.
Judge Pablo Ruz ordered both jailed incommunicado and indefinitely until a date is set for court proceedings, the court statement said.
Ruz said he decided to approve the charges after reviewing evidence provided by the U.S. Justice Department that included information from a witness currently under government protection, French judicial authorities and the police services of Gibraltar and Russia.
The Turk, named in the statement as Cengiz Yalcin, was charged Friday with the possession of explosives and a device
Yalcin worked for years in the construction industry in Gibraltar and the explosive material was seized at his property in the southwestern Spanish city of La Linea, just across the border from the British colony and naval base.
The judge's statement said the two Russians had also been living in La Linea, and that other evidence seized from Yalcin included passport photographs of the Russians and videos that could suggest preparation for a terror attack.
Evidence provided by Russia linked Magomedov with international terrorist organizations and said that he had been in Pakistan and Afghanistan in 2010, the statement said.
Ruz's statement said evidence from the U.S. revealed that Magomedov may have acted under the pseudonym of Muslin Dost, and had been involved in terrorist activity in 2010 in Afghanistan and Waziristan, a lawless mountainous region in the northwest of Pakistan known as a terror training ground.
Both men traveled to France before entering Spain in April or May this year, where they stayed in La Linea. While there both men allegedly took paragliding lessons paid for by Yalcin, the judge said.
The Russians were allegedly heading back to France when police moved in to arrest them in the central city of Ciudad Real. Neither had any identification documents but each is known by several aliases, the statement said.
While Ruz's statement did not reveal the name of the terror organization the Russians are suspected of belonging to, it said both "partially acknowledged" links to it.
Interior Minister Jorge Fernandez Diaz on Thursday described the Russians as suspected al-Qaida members and said the Turk was suspected of being a facilitator for them.
Yalcin was arrested Thursday in La Linea while the Russians were nabbed Wednesday as they traveled by bus from the southern city of Cadiz toward the French border crossing at Irun. Cadiz is very close to the large U.S. military base in Rota alongside the Mediterranean.
No mention was made in the judge's report on whether the suspects may have been planning a terror attack using paragliders, but experts have been concerned that Islamic jihadists bent on attacking Western targets might try to use small planes to target events with many people out in the open.
Fernando Reinares, a former senior anti-terrorism adviser to the Spanish government, said evidence uncovered so far shows "this is not a case of an independent homegrown radicalized cell. This is a local facilitator and two operatives coming from abroad on a mission with a connection to al-Qaida."
Governments and experts in recent years have highlighted jihadists who radicalize on their own without direct connections to terror groups as a growing threat, but Reinares said the Spain case underscores how organized cells with links to known groups are still dangerous.
"The whole story is very serious," said Reinares, now a terror expert with the Elcano Royal Institute in Madrid. "It shows they were trying most likely to target something from the air."
Alan Clendenning contributed from Madrid.