Felipe Irarrazabal, head of the National Economic Prosecutor's office, known by its Spanish initials FNE, met on March 29 with three lobbyists for the Chinese miner to discuss "Corfo's complaint against Tianqi," according to the website.

The meeting at the prosecutor's downtown Santiago office came as the FNE reviewed a complaint filed by Chile development agency Corfo. The complaint seeks to block the sale by Canada's Nutrien Ltd of a 32 percent stake in SQM to Tianqi or any state-backed Chinese bidder.

Tianqi declined to comment on Wednesday.

Chengdu-based Tianqi in late 2017 presented a "non-binding" offer for the stake, according to Eduardo Bitran, former head of Corfo.

The approximately-$4 billion stake in SQM, the world's lowest-cost producer of lithium - a key ingredient in rechargeable batteries - is considered a prize asset in the global race to secure resources to develop electric vehicles.

Corfo, which oversees SQM's lithium leases in the Salar de Atacama, said in the March 9 complaint that the transaction would "gravely distort market competition."

Together, Tianqi and SQM, the world's second-biggest lithium producer after U.S.-based Albemarle Corp, would control 70 percent of the global lithium market, the document said.

The FNE has until August, with the possibility of further extensions, to determine whether to launch a full investigation.

Canadian fertilizer company Nutrien must sell its stake in SQM by next March as part of pledges to regulators who approved this year the merger of Agrium and Potash Corp of Saskatchewan, which created Nutrien. SQM also has significant fertilizer production.

(Reporting by Dave Sherwood; Additional reporting by Tom Daly in BEIJING; Editing by Bernadette Baum and Manolo Serapio Jr.)

By Dave Sherwood