A wide-ranging investigation into generic drug prices took its most significant turn yet on Thursday, as state attorneys general accused two industry leaders, Teva Pharmaceuticals and Mylan, and four smaller companies of engaging in brazen price-fixing schemes — and promised that more charges were coming.

A civil complaint filed by 20 states accuses the companies of conspiring to artificially inflate prices on an antibiotic and a diabetes drug, with executives coordinating through informal industry gatherings and personal calls and text messages. Officials said the case was a small example of broader problems in the drug business.

“We believe that this is just the tip of the iceberg,” George C. Jepsen, Connecticut’s attorney general, whose office started the inquiry that led to the charges, said in an interview on Thursday. “I stress that our investigation is continuing, and it goes way beyond the two drugs in this lawsuit, and it involves many more companies than are in this lawsuit.”

The accusations, as well as continuing investigations at the state and federal levels, have left a cloud of uncertainty over the industry. While several other big generic drug companies have received subpoenas, it is unclear where the inquiries will eventually lead. The generic drug business is already on the defensive and struggling to recover from a barrage of public criticism in the past year over high prices.