* Swiss high court upholds seizure of $1.85 mln in bank accounts
* Case involves transfers to Mongolian former finance minister
* Swiss case comes amid Mongolian probe of Rio Tinto mine deal
ZURICH, March 19 (Reuters) - Switzerland's highest court has upheld the seizure of $1.85 million in Swiss bank accounts, part of a corruption probe linked to a former Mongolian finance minister who helped clear the way for a disputed Rio Tinto mining project, a ruling showed.
The Swiss Office of the Attorney General (OAG) also confirmed it has an ongoing criminal investigation in which prosecutors contend one of the seized accounts was used to transfer $10 million to the ex-minister, Bayartsogt Sangajav.
Anti-graft authorities in Mongolia are investigating the country's 2009 investment pact with Rio Tinto, signed by Bayartsogt, that kickstarted the British-Australian company's Oyu Tolgoi copper-gold project in the Gobi desert.
Neither the OAG nor the heavily redacted Swiss Federal Tribunal ruling, released on Friday, identified Bayartsogt or Rio Tinto by name, but the court documents include details that clearly show both are elements of the OAG's probe.
The court documents refer to Rio Tinto's mine, now undergoing a $5.3 billion expansion, but do not accuse the company of wrongdoing on the project.
A spokesman for the Swiss OAG declined further comment on its investigation, saying it was confidential and adding those being scrutinized are presumed innocent until proven otherwise. Rio Tinto declined comment when contacted by Reuters.
"We confirm the Swiss attorney general's office is conducting a criminal proceeding due to suspicion of bribery of foreign officials and money laundering," the OAG said in an emailed response to Reuters.
Telephone calls and text messages from Reuters to Bayartsogt seeking comment were not answered or returned.
The Swiss attorney general's office launched its probe in 2016, court documents show, when prosecutors seized the bank accounts they say were linked to a transfer of 8.2 million euros ($10.1 million) to accounts controlled by Bayartsogt in September 2008, the month he became Mongolia's finance minister.
Since then, the unidentified owner of the seized accounts, with a balance of some $1.85 million, has sought unsuccessfully to have the funds unfrozen.
The account holder contended there was insufficient suspicion to make a case, that Switzerland lacks jurisdiction, that the statute of limitations had expired and that he had diplomatic immunity from criminal prosecution, court documents show.
In its rejection of those claims published on Friday, the Federal Tribunal's three-judge panel wrote that evidence pointed to "concrete clues that large amounts of money of questionable origin" had flowed in transfers that were "typical of money laundering."
"It is very suspicious that the minister of a foreign country, immediately after taking a ministerial post, would be the recipient of such a large sum," the ruling said, adding the OAG's criminal probe remains in its early stages.
A spokeswoman for Mongolias anti-corruption authority told Reuters that it is investigating a number of cases involving Bayartsogt. She did not elaborate.
A Swiss lawyer representing the holder of the seized accounts did not reply to an email seeking comment.
The Swiss Federal Tribunal's ruling also referenced allegations that have been raised by some Mongolian politicians, accusing the government of handing too much control over big mining projects to foreign interests like Rio Tinto.
"There are indications that (Bayartsogt) as finance minister signed a contract that was disadvantageous to the Mongolian state," the Swiss ruling said.
In 2013, Bayartsogt resigned as deputy speaker of the Mongolian parliament after details emerged of his Swiss bank account in reports by the International Consortium of Investigative Journalists, the group that has written extensively about leaks including the Panama Papers.
($1 = 0.8139 euros) (Reporting by John Miller in Zurich, Barbara Lewis in London and Munkhchimeg Davaasharav in Ulaanbaatar; Editing by Dale Hudson)