HONG KONG, June 17 (Reuters) - China’s market regulator has begun an antitrust probe into Didi Chuxing, three people with knowledge of the matter said, just as the ride-hailing giant is pushing ahead with what could be the largest initial public offering in the United States this year.

The probe, reported here for the first time, is the latest in a sweeping crackdown on China's so-called "platform" companies, including Alibaba Group Holding Ltd (9988.HK), and Tencent Holdings Ltd (0700.HK).

China's market regulator, the State Administration for Market Regulation (SAMR), is investigating whether Didi used any competitive practices that squeezed out smaller rivals unfairly, two of the three sources said.

In its IPO prospectus made public last week, Didi disclosed that it and more than 30 other Chinese internet companies had met with regulators, including the SAMR, in April.

Two of the sources familiar with the situation said that the probe by the markets regulator was in the initial stages, and that the regulator was yet to give the company detailed instructions.

firm currently owns 12.8% stake in Didi, according to the Chinese company's prospectus.