Ten people have been arrested in the United States for allegedly spying for the Russian government.
The US Department of Justice said they were held for allegedly carrying out “long-term, 'deep-cover' assignments” on US soil.
They have been charged with conspiracy to act as unlawful agents of a foreign government, a crime which carries up to five years in prison.
An 11th suspect remains at large, according to justice officials.
The BBC's Kim Ghattas in Washington says it is a story of Cold War-era espionage with the tools and technology of the 21st Century.
The alleged agents were trained by the Russian Foreign Intelligence Service (SVR) and sent to the US to infiltrate policy-making circles and collect information, according to court papers filed in US District Court for the southern district of New York. Some of them had been living in the country under false identities since the early 1990s, using codes and and engaging in advanced computer operations, including posting apparently innocent pictures on the internet which contained detailed texts, investigators say.
The FBI also reported observing older techniques, such as money being buried next to a beer-bottle marker and “brush pasts” in parks.
“You were sent to USA for long-term service trip,” says one purported message to two of the suspects that was intercepted by US intelligence. “Your education, bank accounts, car, house etc – all these serve one goal: fulfil your main mission, ie to search and develop ties in policymaking circles in US and send intels.”
They allegedly got close to a scientist involved in designing bunker-busting bombs and a top former intelligence official.
Five of the suspects will appear later in a Manhattan federal court – a couple known as “Richard Murphy” and “Cynthia Murphy”, who were arrested in Montclair, New Jersey; Vicky Pelaez and a man known as “Juan Lazaro,” who were arrested in Yonkers, New York state; and Anna Chapman, who was arrested in Manhattan, New York City.
Another three – Mikhail Semenko and a couple known as “Michael Zottoli” and “Patricia Mills” – will appear in a federal court in Alexandria, Virginia, after being arrested in Arlington, Virginia.
The final two people – a couple known as “Donald Howard Heathfield” and “Tracey Lee Ann Foley” – were arrested in Boston, Massachusetts, and will appear in a federal court in the city.
A suspect known as “Christopher R Metsos” remains at large.
All of the arrested suspects, except Ms Chapman and Mr Semenko, have also been charged with conspiracy to commit money laundering, which carries a maximum penalty of 20 years in prison.
Our correspondent says the arrests will come as quite a surprise, as relations between Washington and Moscow have warmed considerably in recent months. Just last week, Russian President Dmitry Medvedev was in Washington having lunch with President Barack Obama.
It is still unclear how the White House will react or how Russia will explain this, she adds.