NEW YORK, Sept 8 (Reuters) - Two proposed mergers of U.S. health insurers worth tens of billions of dollars would hurt competition in commercial health plans in as many as 17 states, the American Medical Association, the U.S. group that represents physicians, said on Tuesday.

Aetna Inc announced plans to buy smaller rival Humana Inc in early July and Anthem Inc agreed to buy Cigna Corp later that month. Both mergers are being reviewed by federal antitrust regulators as well as state insurance officials.

Insurers say that the deals will enable them to offer more competitive health insurance plans by using their increased size to negotiate better prices with doctors.

Anthem and Cigna combined would increase market power in 13 states where they sell individual insurance plans and competition would decrease in all 14 states where Anthem currently operates Blue Cross Blue Shield plans, the AMA's analysis found.

Aetna and Humana combined would raise anti-competitive issues in 7 states on an individual basis and 14 states overall, the study said.

The study was based on 2013 data on enrollment in commercial fully insured and self insured plans, the association said.

The American Hospital Association also recently made public its analysis of the two deals, also saying they would diminish competition.

(Reporting by Caroline Humer; Editing by Frances Kerry)