Washington has announced the successful completion of its biggest spy swap with Russia since the Cold War.
Ten Russian agents were flown to Vienna hours after they admitted in a US court to being agents for a foreign country.
A Russian jet carrying four prisoners freed by Russia arrived around the same time.
The American plane later flew on to a UK air base, where several people were seen getting off, while the Russian aircraft flew to Moscow.
Television pictures from Vienna showed the two aircraft parked side by side on the runway. Covered aircraft stairs were brought up to both planes and none of the agents could be seen being transferred.
A swap at the airport would mean that no-one had officially entered the country.
The lawyer for nuclear specialist Igor Sutyagin, one of those released by Russia, confirmed that his client had left Moscow, Austrian media said.
Russia's foreign ministry acknowledged the swap, saying it would mean the "return to Russia of 10 Russian citizens accused in the United States, along with the simultaneous transfer to the United States of four individuals previously condemned in Russia".
About 90 minutes passed between the arrival of the two jets in Vienna and their departure.
The US plane, a Vision Airlines Boeing 767-200 which had flown to Vienna from New York, later made a stop-over at Brize Norton RAF base in Oxfordshire, England.
It was unclear whether any of the four prisoners freed by Moscow would stay in the UK or fly on to another country. When the plane took off again, its destination was unknown.
Russia's Yak-42 government jet landed in Moscow's Domodedovo airport where people could be seen getting off and being transferred to a bus.
The assumption is that the 10 spies will now be debriefed by the Russian authorities and will be kept away from the media for the time being, the BBC's Rupert Wingfield-Hayes reports from the airport.
The 10 Russian agents earlier pleaded guilty in New York to "conspiracy to act as an unregistered agent of a foreign country". More serious money laundering charges against them were dropped.
Their New York court appearance was the first time they had all appeared in public together since being arrested last month.
Prosecutors said the accused had posed as ordinary citizens, some living together as couples for years, and were ordered by Russia's External Intelligence Service (SVR) to infiltrate policy-making circles and collect information.
BBC Washington correspondent Kevin Connolly says there is broad agreement in the US that the agents are being deported swiftly because neither government wants this to damage attempts to reset their often prickly relationship.
Court documents revealed the real names of five of the Russians involved.
The US state department said after the hearing that there would be "no significant national security benefit" in sentencing the 10 to lengthy jail terms.
"The network of unlawful agents operating inside the United States has been dismantled," spokesman Mark Toner said.
"The United States took advantage of the opportunity presented to secure the release of four individuals serving lengthy prison terms in Russia, several of whom were in poor health."
The lawyer for Anna Chapman - also known as Anya Kushchenko - played down the importance of the Russian group's espionage in the US.
Robert Baum told Associated Press: "None of the people involved from my understanding provided any information that couldn't be obtained on the internet."
A lawyer for another suspect, Vicky Pelaez, said a Russian official had told his client she would receive $2,000 a month for life and free housing in Moscow.
But the lawyer, John Rodriguez, added she would be allowed to leave Russia if she wanted to - and he indicated she would return to Peru.
The Russian foreign ministry said the exchange by Russia's Foreign Intelligence Service and the US Central Intelligence Agency was being conducted in the context of "overall improvement of the US-Russian ties and giving them new dynamics".