SHANGHAI (Reuters) - HHLR Management, part of Chinese investment giant Hillhouse's public investment arm, raised its stake in solar energy firm LONGi Green Energy Technology to 5% on Friday as it moves to reverse share selling that had invited a regulatory probe, LONGi said.

HHLR was placed under investigation last November for a possible violation of share transfer rules as China's securities regulator tightened scrutiny over stock selling to revive a flagging market.

The firm has been actively cooperating with regulators' probe, and will in the next month buy back all the shares offloaded in the probed selling, LONGi said.

In an exchange filing on Friday, LONGi said HHLR had increased its stake to 5% from 4.98% on the day. Under Chinese rules, an investor is obliged to disclose ownership when it hits 5%.

Hillhouse is controlled by billionaire Zhang Lei.

(Reporting by Shanghai newsroom; Editing by Jan Harvey)