Some of the nation's largest airlines are raising fares by up to $10 per round trip, the first broad increase in three months.

Sister airlines United and Continental raised prices on many U.S. routes by $4 to $10 per round trip, and Delta matched the increase, spokesmen for the airlines confirmed. Officials at American Airlines and JetBlue Airways said on Friday afternoon they had not raised prices.

Other airlines did not comment immediately. U.S. airlines raised domestic prices a half-dozen times in early 2011 to boost revenue and cover rising jet fuel costs, but the last broad increase was in April.