MOSCOW - Russia's domestic intelligence agency said on Tuesday it had established the guilt of a man Russian media have identified as the spymaster who betrayed a ring of agents operating in the United States last year.

Russian media have reported that a top spy they identified as Alexander Poteyev was responsible for betraying 10 Russian agents deported from the United States and handed back to Russia in a Cold War-style swap at a Vienna airport in July.

Poteyev, described in media reports as a colonel in foreign intelligence and deputy chief of the department that ran spies operating in the United States without diplomatic cover, was reported to have fled to the United States days before the spy ring was arrested.

The Federal Security Service (FSB) told Russia's three main news agencies on Tuesday military prosecutors had sent a case against "Russian Federation citizen A. N. Poteyev" to court on April 21 after FSB investigators determined he was guilty of treason and desertion.

The FSB declined to comment further.

The arrest of the spy ring in the United States was a huge embarrassment for Russia's intelligence services. The Russians admitted being agents and were swapped for four Russians imprisoned at home on charges of spying for the West.

One of the four, Igor Sutyagin, on Tuesday won a case against Russia in the European Court of Human Rights.

The court ruled he had been denied the right to a fair trial and held too long before his trial following his jailing in 1999.

Sutyagin, a nuclear weapons expert, was sentenced to 15 years in prison in 2004 on a treason conviction for passing information to a British firm prosecutors said was a CIA front.

Sutyagin denied the charges, saying the information was available from open sources, and Kremlin critics said his conviction was part of a crackdown on scholars with Western ties under Vladimir Putin, president at the time.

Sutyagin and three other Russians were pardoned by President Dmitry Medvedev before the swap. Freed after nearly 11 years in prison, Sutyagin was flown to Britain, where he remains.

Putin, a longtime Soviet KGB officer and former FSB chief who is now prime minister, moved carefully to avert damage to warming ties with Washington.

Putin and other officials have in the past suggested that a turncoat's betrayal lay behind the arrests. Putin warmly welcomed the agents upon their return and warned that those who betrayed their compatriots would end up paying a heavy price.

In November, respected Russian daily Kommersant cited a Kremlin official as saying the government knew the identity and location of the person who blew the Russian agents' cover.