New York's attorney general is investigating whether insurance companies may be unfairly limiting coverage for a costly drug

The tussle over costly cures for hepatitis C - a chronic, blood-borne infection that can lead to cirrhosis and liver cancer and affects between 130 and 150 million people worldwide - has turned toward a new target: health insurers.

The New York state attorney general's office on Wednesday asked 16 health insurers for information related to patients who've been denied hepatitis C drugs, Reuters reported. Their concern is that insurers are limiting coverage just to those who are the most sick.

The Attorney General's office also asked for details on how health insurance companies go about authorizing the use of hepatitis C drugs, Reuters reported.

The subpoenas went out to health insurers, including Aetna Inc, CareConnect and EmblemHealth Inc, the person said.

The initial two subpoenas from Schneiderman's office asked for information only about the hepatitis C drug Harvoni, while the remaining subpoenas didn't specify any particular drug, the person familiar with the matter said.

Gilead Sciences Inc, with its two blockbuster drugs Harvoni and Sovaldi, has dominated the market for hepatitis C. Harvoni's total sales were $13.86 billion in 2015. The drugs, which cure the disease in typically less than 12 weeks, have a list price of at least $84,000 per course of treatment. Pharmaceutical company AbbVie also makes a competitor that comes in at $83,319. In January, a third cure was approved - Zepatier - which costs $54,600 per treatment.

The high costs of the cures have put insurers in a tough spot: Because hepatitis C is a chronic condition, should all patients be treated immediately, or should those who have progressed farther get priority to the costly medication while others hold off so the expense is not all upfront?

This isn't the first time the drug's high cost has come into question: In January, Massachusetts' attorney general asked the biotechnology company to reconsider its pricing for Sovaldi and Harvoni. The Gilead drugs were also the subject of an 18-month Senate investigation that concluded that the company put profits ahead of patients when deciding on the price of Sovaldi and Harvoni.

(Reuters reporting by Sarah Lynch in Washington and Vishal Sridhar in Bengaluru)