New York (AFP) - The FBI eavesdropped on the activities of Russian spies in New York for months with the help of tiny recorders planted in binders purportedly containing trade secrets, US court documents show.

The revelations were made in papers filed by prosecutors on Tuesday in the case of an alleged Russian spy, Evgeny Buryakov, who goes on trial April 4 accused of working undercover for Moscow while masquerading as a New York banker.

Buryakov, who was arrested in January 2015, is accused of working with two other spies, who were attached to the Russian trade and UN missions in New York and have since left the country. He has pleaded not guilty.

From January to May 2013, an undercover FBI agent brought binders of purported oil and gas analysis that also contained "covertly placed recording devices" to meetings with one of the Russian spies.

The US agent told the Russian the files were confidential and claimed he would be sacked if anyone found out he had disclosed the information, so asked for them to be returned promptly, the court document said.

The technique allowed the FBI to listen for hours to Russian spies as they received tasks from Moscow, gathered responses and fed information back to Russia's SVR foreign intelligence agency from January to May 2013.

It was thanks to these tiny bugs that they heard them complain that the humdrum nature of their work was removed from the adventure of James Bond films.

One was heard saying he thought it "would be just slightly more down to earth than in the movies about James Bond." He hoped to have been "at least" operating under a false identity, the court papers show.

The FBI agent was approached by one of the Russians for information about the oil and gas industry in 2012. The Russian gave him cash or gifts in exchange.

Officials said the net closed in on Buryakov after he met numerous times in 2014 with an FBI source posing as the representative of a wealthy investor looking to develop casinos in Russia.

The other two spies, Igor Sporyshev and Victor Podobnyy, were protected by diplomatic immunity and have left the United States.

Buryakov's arrest was the first such case since 10 deep-cover agents including Anna Chapman, were arrested in the New York area in 2010. They pled guilty and were part of a prisoner swap with Moscow.