(Adds details, background) BENGALURU, March 2 (Reuters) - U.S....

(Adds details, background)

BENGALURU, March 2 (Reuters) - U.S. boutique investment firm GQG Partners has bought shares worth $1.87 billion in India's Adani group companies, the conglomerate said on Thursday, marking the first major investment in the group since a short-seller's critical report sparked a stock rout.

The group's seven listed companies have lost some $135 billion in market value since Jan. 24, when Hindenburg Research accused it of improperly using offshore tax havens and of stock manipulation - allegations the billionaire Gautam Adani-led group has denied.

GQG Partners, through block deals, has bought shares worth 154.46 billion rupees in Adani Ports and Special Economic Zone APSE.NS , Adani Green Energy ADNA.NS , Adani Transmission ADAI.NS and the conglomerate's flagship firm Adani Enterprises ADEL.NS , a regulatory filing on Thursday showed.

"We believe that the long-term growth prospects for these companies are substantial," said Rajiv Jain, chairman and chief investment officer of GQG Partners.

"We are pleased to be investing in companies that will help advance India's economy and energy infrastructure, including their energy transition over the long-run."

Jefferies India was the sole broker for the transaction.

($1 = 82.5180 Indian rupees)