MELBOURNE, March 29 (Reuters) - Australia's securities regulator searched the offices of coal miner TerraCom Ltd on Monday with assistance from Queensland state police, according to a report in the Australian Financial Review.

The probe comes after the regulator confirmed it was investigating testing laboratory ALS, whose internal review last year found that about half the certificates it provided for export coal samples over the past decade had been altered to improve the quality indicated.

The laboratory's review did not name any counterparties, but it was initiated following an unfair dismissal case brought against TerraCom - which bought the Blair Athol coal mine in 2017 from Rio Tinto - that the miner had worked with ALS to falsify export documentation.

TerraCom, which sells coal to Japan, Korea and China, has denied the allegations that came out in the case. Deputy Chairman Craig Ransley told Reuters that TerraCom would continue to cooperate with authorities in the industry wide probe.

Australia is the world's biggest coal exporter and ALS is among the biggest testers of coal. "I can confirm a warrant was executed today on behalf of ASIC, with Queensland Police assisting," said a spokesman for the Australian Securities and Investments Commission (ASIC), without naming TerraCom.

Queensland Police, asked if TerraCom's Blair Athol operations had been searched, said ASIC was leading the matter and referred any questions to the regulator.

Last week, local media reported that ASIC Commissioner Cathie Armour said during a Senate estimates hearing she was "very much aware" of allegations that laboratory ALS had inflated coal quality results on export certificates.

Armour offered no further information due to ASIC's policy of not commenting on matters under inquiry, according to a report by the Australian Associated Press. South Korean power provider Korea South-East Power banned ALS from certifying its coal tenders last year. (Reporting by Melanie Burton; Editing by Tom Hogue)