The head of the FCC's Wireless Telecommunications Bureau has resigned after a tumultuous one-year term.

Rick Kaplan handled the Commission's review of AT&T's failed merger with T-Mobile and led the eventual decision to block the transaction.

He is also leading the agency's review of Verizon Wireless' purchase of AWS spectrum from Comcast, Time Warner Cable, Bright House Networks and Cox Communications.

The reason for Kaplan's departure, effective mid-June, was not provided in today's announcement.

Kaplan was appointed to his position just last June, when then bureau chief Ruth Milkman left to take a post as special counsel for innovation in government for FCC Chairman Julius Genachowski.

Kaplan previously served as Genachowski's chief legal counsel during a period when the agency was tasked with reviewing Comcast's takeover of NBCUniversal.

Milkman will succeed Kaplan, returning to her former role as head of the wireless bureau. In her new post, Milkman "will continue her engagement in the implementation of incentive auctions," the FCC said.

Kaplan's resignation comes after the FCC said last week that general counsel Austin Schlick would leave his post in June. Schlick, who led reform efforts such as expanding access to Commission documents, will be replaced by Sean Lev, currently serving as deputy general counsel and special advisor to Genachowski.