Ten people pleaded guilty today to being unregistered foreign agents for Russia while living undercover in the United States.
The plea deal in federal court could be part of a swap of imprisoned spies between the US and Russian governments. US counter-intelligence authorities arrested the group last month on suspicion of trying to infiltrate US policymaking circles.
Earlier, the brother of a jailed Russian nuclear expert said Moscow would free him and send him to Vienna today in the first stage of a spy swap with the United States, but neither side confirmed the Cold War-style deal.
It was unclear if Igor Sutyagin, convicted in 2004 of passing secrets to the West, had already arrived in the Austrian capital as part of what his lawyer says could be an exchange for alleged Russian agents arrested in the United States.
Rights activist Ernst Chorny said Mr Sutyagin's father had received a call from a Western television company and was told Sutyagin had been seen arriving in Vienna and being met by a British officer.
"I do not have objective information myself," Mr Chorny said by telephone.
An Austrian foreign ministry spokesman said: "I can neither confirm nor deny that he has arrived. We have no further information."
In a scandal that drew global headlines, US counter-intelligence authorities arrested 10 people last month on suspicion of being members of a Russian spy ring that was trying to infiltrate policymaking circles in the United States.
The Kremlin and the administration of President Barack Obama have sought to prevent the arrests from causing a new chill in ties between the Cold War foes, which have improved after hitting lows with Russia's 2008 war against Georgia.
A lawyer for Sutyagin, Anna Stavitskaya, said yesterday that Moscow wanted to bring the alleged agents back to their homeland by offering an exchange involving Sutyagin and other prisoners in Russia.
Later yesterday, a US official who spoke on condition of anonymity told Reuters that Washington might allow the suspected Russian agents to plead guilty and then return to Moscow in exchange for the release of certain Russian prisoners.
A Russian special forces unit used to transport high-security prisoners arrived at Lefortovo on Thursday, and Sutyagin's family said he was due to fly to Vienna.
"We know he is supposed to go to Vienna today for the swap," his brother Dmitry said.
But Dmitry Sutyagin later said that he had did not know where his brother was.
"All we have is a wave of rumors, we have no objective information," he told Reuters.
Russian authorities were tight-lipped.
"We are not commenting at all, neither confirming nor denying these reports about a spy swap," a spokesman for Russia's Foreign Intelligence Service (SVR) said by telephone.
Reuters