MIAMI (AFP) - A Mexican has been arrested in the US city of Miami for spying on "a US government source" on behalf of Russia, the Department of Justice alleged on Tuesday (Feb 18).

Hector Alejandro Cabrera Fuentes, a Mexican citizen who lives in Singapore, is accused of conspiracy and "acting within the United States on behalf of a foreign government".

US intelligence officials have identified Russia as a central spying threat to the country, and Special Counsel Robert Mueller's investigation last year found that Moscow interfered in the 2016 presidential election - a finding that President Donald Trump has repeatedly dismissed.

According to court documents cited in a Department of Justice (DOJ) news release, a Russian government official recruited Fuentes last year and told him to rent a specific property in Miami-Dade County, not using his own name.

Fuentes allegedly travelled to Russia, where he told the government official about the arrangements.

On a subsequent trip this month, the Russian official "provided Fuentes with a physical description of a US government source's vehicle and told Fuentes to locate the car, obtain the source's vehicle licence plate number, and note the physical location of the source's vehicle," DOJ alleged.

Last week, Fuentes travelled to Miami from Mexico City and drove to the residence of his target, where a security guard stopped him, but his companion managed to photograph the target's licence plate, the court documents said.

When the pair tried to leave Miami for Mexico City on Sunday, US Customs and Border Protection allegedly found images of the photo in their phones.

"According to court documents, messages on Fuentes's phone showed that the Russian official initiated and directed the meetings," the DOJ statement said, without giving any further detail about the US source targeted.

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Fuentes is to appear in court for a pretrial detention hearing on Friday, followed by his arraignment on March 3.