WASHINGTON — The Obama administration announced on Wednesday that it was imposing sanctions on North Korea’s leader, Kim Jong-un, personally, blacklisting the unpredictable ruler and top officials in his reclusive government for human rights abuses as he aggressively presses forward with his nuclear and ballistic missile programs.

The State Department took the unusual step of naming Mr. Kim and 14 other senior officials it said were responsible for grave human rights abuses in a five-page report detailing repression in North Korea. The report singled out top figures inside its intelligence and security ministries, which the department said had engaged in practices including extrajudicial killings, forced labor and torture.

The Treasury Department, imposing its first human rights sanctions on any North Korean official, designated them on a list of people whose assets are frozen and who are barred from transactions with any American citizen.

The actions were mandated by Congress as part of a law enacted in February that required the administration to report on human rights abuses in North Korea and to impose sanctions on anyone found to be responsible. But senior administration officials said they had long planned to take more aggressive action that would move human rights violations — until now on the periphery of the United States’ efforts to isolate and punish North Korea for its bad behavior — to a more central position in the administration’s strategy. That involved a painstaking, monthslong process of identifying the officials inside North Korea’s secretive system who were the worst offenders.