A court in Russia has upheld a decision to keep a US-Irish citizen accused of spying in custody while he awaits trial.

Paul Whelan was arrested on Friday, December 28th.

Originally described by Russian authorities as a US citizen, the 48-year-old is accused of being caught while on a 'spy mission'.

Although he lives in the US, it has emerged that he also holds Irish, Canadian and British passports.

Following a request from Mr Whelan's lawyer to release the suspect on bail, Russian state media today reports that the request has been denied.

Moscow City Court upheld an original decision to remand Mr Whelan in custody.

The appeal is reported to have been held behind closed doors, as authorities say the case involves classified data.

Meanwhile, the TASS news agency reports that Mr Whelan's lawyer said his client may have inadvertently received classified data on a storage device.

Vladimir Zherebenkov said: "Whelan received secret data on a flash card, but he expected to get open source information of cultural importance."

A number of other media outlets quote Mr Zherebenkov as saying Mr Whelan had been expecting to receive holiday photos on the flash drive.

The lawyer added that they intend on appealing the court's latest decision to keep Mr Whelan in detention.

Mr Whelan is employed in the US by automotive company BorgWarner as director of global security.

The Washington Post has reported that Mr Whelan had previously served as a US Marine, but was discharged for bad conduct in 2008 "after being convicted of several charges related to larceny".

The Department of Foreign Affairs here has previously said it is ready to provide "all possible and appropriate assistance" in the case.