The lawmaker father of a Russian man detained by the US on hacking charges warned Friday his son would die without medical help, raising the stakes in the latest spat between Moscow and Washington.

Russia has accused US authorities of abducting Roman Seleznev in the Maldives and secretly transporting him to the American territory of Guam in a case that further piqued Kremlin's anger amid a showdown over Ukraine.

The 30-year-old man is suspected of being one of the world's most prolific traffickers of stolen credit card details.

He is accused by US authorities of hacking into retail computer systems and installing malicious software to steal credit card numbers between October 2009 and February 2011.

His father, Valery Seleznev, a lawmaker in the fiercely anti-Western ultra-nationalist Liberal Democratic Party, told a news conference his son was disabled and could die within days if he did not receive regular medical treatment.

Roman Seleznev suffered brain damage in a bomb attack in Morocco in 2011 and has problems with motor skills, according to his family.

"If he does not take it (medication) for three, five days at the most then... he would die and die very soon," Valery Seleznev said.

"One of the goals is to let him rot there."

Russia's foreign ministry on Friday released what it said were "shocking new details" of Roman Seleznev's arrest, saying he was bundled onto a private plane in handcuffs by three US secret service agents as he tried to board flight to Moscow in Male airport.

Valery Seleznev said the people who detained his son posed as tourists and wore shorts and backpacks.

"No legal procedures with the participation of local authorities that are necessary for extradition were conducted," the ministry said in a statement.

"As a result, his health and life are under threat," the statement said, adding that Roman Seleznev was being kept in a cold cell.

Maldivian President Abdulla Yameen has said his government acted alone in expelling the suspect, stressing it was responding to an Interpol arrest warrant.

- 'Sticking to his guns' -

Roman Seleznev and his accomplices are accused of stealing over 200,000 credit card numbers in a scheme that cost banks more than $1.1 million (800,000 euros), according to a 2011 indictment.

If convicted, he faces up to 30 years in prison on bank fraud charges and additional jail time for other charges.

According to US officials, the suspect was known under the moniker "Track2" in the hacker underground.

Valery Seleznev said US officials were pressuring his son to incriminate himself.

He dismissed the charges, saying his son was not a hacker and knew "nothing about these new technologies".

"My son is sticking to his guns," he said. "Right now they are piling pressure on him."

"The lawyers describe the (current) prison as one of -- and maybe the worst -- prison under US jurisdiction," he said, adding that officials had promised to transfer him to Seattle if he admitted guilt.

Russia's foreign ministry has called the detention a "hostile" act and said its diplomats were expected to visit Roman Seleznev in prison on Monday.

Moscow has said the man's "abduction" is the latest in a string of unlawful arrests of its nationals by the US, including so-called "merchant of death" Viktor Bout, who was sentenced to 25 years over arms trafficking.

A cybercrime expert, who spoke to Russia's Novaya Gazeta newspaper on condition of anonymity, suggested that the US Secret Service may be behind the suspect's detention.