House Armed Services Committee Chairman Howard "Buck" McKeon (R-Calif.) in April 2012. (J. Scott Applewhite/AP)

Update 10:22 a.m. Thursday: McKeon has made it official, announcing his retirement and endorsing Thornberry for chairman of the Armed Service Committee.

Rep. Buck McKeon (R-Calif.), chairman of the House Armed Services Committee, is set to announce that he won't seek reelection in 2014, according to two people with knowledge of his plans.

McKeon's retirement has been rumored for a long time, and his office said he would make an announcement in the New Year. His office declined Wednesday to confirm his retirement.