Ten Russian spies were exchanged for four agents working for Western services at Vienna airport on Thursday, the Russian Foreign Ministry said, confirming one of the biggest swaps ever between Washington and Moscow.

Russia’s Foreign Intelligence Service and the U.S. Central Intelligence Agency carried out the operation, the ministry said shortly after an airplane from Russia’s Emergency Ministry and a plane from U.S. carrier Vision Airlines took off from Vienna.

Both aircraft had arrived at Austria’s capital around an hour earlier from their respective countries and parked side by side to swap the ten spies who were active in the U.S. against the four who had operated in Russia.

“This action was carried out in the general context of improving Russian—US relations and giving them a new dynamic in the spirit of the agreements in principle at the highest level between Moscow and Washington on the strategic nature of Russian—U.S. partnership,” the ministry said.

The exchange came after Russian President Dmitry Medvedev pardoned four men early Friday after they admitted their guilt.

The four includes Igor Sutyagin, a private nuclear researcher, who arrived in Vienna on Thursday, according to media reports. The U.S. has disputed his guilt.

The others are double agents Alexander Zaporozhsky and Sergei Skripal, as well as Gennadi Vasilenko.

The U.S. deported 10 people of Russian origin who pleaded guilty on Thursday in New York federal court of spying for Russia.

During the proceedings, the 10 spies admitted their guilt. Seven of them who had been operating under fake names admitted their true identities.

These included Richard and Cynthia Murphy, who lived in New Jersey, and were the parents of an 11 and a seven—year—old. Their real names were Vladimir and Lydia Guryev.

Michael Zottoli and Patricia Mills, who lived with their one and three— year—olds in Virginia, said their true identities were Mikhail Kutsik and Natalia Pereverzerva.

Donald Howard Heathfield and Tracey Lee Ann Foley, who lived with two teenagers in Boston, conceded their names were Andrey Bezrukov and Elena Vavilova. Juan Lazaro, who lived with his wife Vicky Pelaez and at least one teenage son in Yonkers, New York, said his real name was Mikhail Anatonoljevich Vaseknov.

Pelaez and two others — Anna Chapman and Mikhail Semenko — were operating under their real names.

Chapman’s lawyer has said that she wants to live in Britain in the future. Pelaez plans to return to her native Peru.

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