Health insurers will be required to justify annual premium increases of 10% or more to state regulators starting in September under a new rule issued by the Obama administration. Federal officials, pointing out that the average cost of health insurance has more than doubled over the last decade, said the effort would help states curb unreasonable rate proposals for millions of individual insurance buyers and small businesses. The new rule will allow regulators to review rate hikes but does not give them authority to reject those found to be unreasonable. It also requires insurers to explain the reasons for increases of 10% or more to the public and to post the justifications on the Internet. Health and Human Services Secretary Kathleen Sebelius predicted that public pressure from the review process will keep insurance costs in line.