In letters sent to Delta Air Lines Inc (>> Delta Air Lines, Inc.), United Continental Holdings Inc (>> United Continental Holdings Inc), American Airlines Group Inc (>> American Airlines Group Inc) and Southwest Airlines Co (>> Southwest Airlines Co) in late June, Connecticut Attorney General George Jepsen said the state is "significantly concerned" about the state of competition in the airline industry.

"It appears that the major airlines have uniformly decided not to increase capacity - perhaps in an effort to keep ticket prices high and maintain their record profit margins, all at the expense of consumers," Jepsen said in the letters, a copy of which were reviewed by Reuters.

Jepsen said he is acting because of concern that competitors in the airline market may have been "improperly coordinating with one another."

News of the state probe comes after the U.S. Justice Department said it is investigating possible antitrust violations by the U.S. airlines. It did not specify which airlines were being probed.

Jaclyn Falkowski, a spokeswoman for the Connecticut AG, declined further comment.

(Reporting by Karen Freifeld and Soyoung Kim)