MADURAI, India — Adani Group’s energy and infrastructure deals across Asia could come under intense scrutiny after U.S. authorities indicted the Indian conglomerate’s billionaire founder in a bribery and securities fraud case, observers say.

News of the charges against Gautam Adani, one of the world’s wealthiest men, and a half dozen others including his nephew shaved more than $26 billion off the market value of the ports-to-telecom group, followed by credit rating downgrades.