Churchill Mining's Indonesia subsidiary offices were among the top four floors at Wisma Kosgoro building which were damaged by a major fire last Monday. Police and firefighters are still investigating the cause of the blaze.

Churchill has been fighting an arbitration dispute with the Indonesian government over one of the world's biggest undeveloped coal reserves in East Kalimantan since 2012 and expects a decision sometime next year, company chairman David Quinlivan told Reuters on Monday.

Churchill's arbitration case is over the ownership of a 350-square-km (135-square-mile) mine site in East Kutai that is estimated to contain 2.8 billion tonnes of coal reserves.

"It is still likely that it will be 2016," Quinlivan said about the international arbitration's conclusion. "We are supremely confident."

Quinlivan said the fire at the company's Jakarta office follows a police raid on the same office last year.

"It's our main office in Indonesia and all of a sudden there was a fire started and (the) reasons are unknown," Quinlivan said by telephone in Perth. "It was the main source of our Indonesian documents."

"This is another one of those coincidences that happens -- just like the police raid on the office last year (that) was timed when there was an (arbitration) document examination occurring in Singapore," he added. "Lots of coincidental things happening."

Churchill's office was raided last September by police, who seized computers and hard copy documents while looking for evidence of alleged forgery of documents. No charges have followed the raid, Quinlivan said.

Indonesia, which is the world's top thermal coal exporter, is currently looking at ways to increase foreign investment at a time when the economy is growing at the slowest pace for five years.

The Churchill case is unlikely to help attract the large infrastructure project investments that president Joko Widodo has said is a key focus for his government.

"I hear from our Indonesian colleagues that the new president is somewhat annoyed that this case is here, running and a distraction to his foreign investment plans and ability to source capital for major infrastructure projects," Quinlivan added.

Indonesia's attorney general's office was unable to give an immediate comment on Monday.

(This version of the story corrects paragraph 5 to show arbitration expected to conclude in 2016, not 2017)

(Additional reporting by Dennys Kapa; Reporting by Michael Taylor; Editing by Tom Hogue and Michael Perry)

By Michael Taylor