The Federal Office of Justice said it received the Russian extradition request on Tuesday, based on a warrant issued on May 14 by a Moscow court.

Russian prosecutors are investigating Adamov for alleged fraud during his time as a minister, the office said.

The United States is also seeking his extradition, but has not yet lodged a formal request for his extradition and has until June 30 to do so, the office said.

Adamov was arrested in Switzerland on May 2 on a warrant issued by authorities in the United States, where he has been indicted on suspicion of financial fraud and money laundering.

He is suspected of embezzling nine million dollars in US funding destined to help Russia improve its nuclear safety.

In the United States, Adamov faces up to 60 years in prison and a fine of 1.7 million.

On Wednesday, his Swiss lawyers said he had lodged an appeal against his detention, claiming it was out of line with a pan-European accord on judicial cooperation as well as with Adamov's immunity, which he enjoys as a former minister.

Adamov was in charge of Russia's nuclear energy portfolio from 1998 to 2001.

It was not immediately clear which of the two extradition requests would take priority.

"That will be examined in the course of the extradition proceedings," Swiss justice spokesman Folco Galli told AFP. "The date of the extradition request is one of the criteria, but not the only one."

Under the terms of international treaties, if more than one state requests extradition, the country holding the detainee must consider various factors.

They include the relative seriousness of the alleged offences, the date of the extradition requests and the nationality of the detainee.