SEOUL, Aug 31 (Reuters) - North Korea conducted a simulated "scorched-earth" nuclear strike on targets across South Korea, state media reported on Thursday, in reaction to allied exercises that it said amounted to plans for a preemptive nuclear attack by the United States.

The missile unit fired two ballistic missiles and correctly carried out its "nuclear strike mission," the General Staff of the North's Korean People's Army (KPA) said in a statement carried by the news agency KCNA.

"The KPA staged a tactical nuclear strike drill simulating scorched-earth strikes at major command centers and operational airfields of the 'ROK' military gangsters on Wednesday night," it said, using initials of South Korea's official name, the Republic of Korea.

North Korea fired two short-range ballistic missiles into the sea on Wednesday, South Korea's military said, hours after the U.S. deployed B-1B bombers for allied air drills.

The latest launch came a day before South Korea and the U.S. wrap up 11 days of combined military drills, which Pyongyang has long denounced as a war rehearsal.

North Korean leader Kim Jong Un on Tuesday observed part of a drill that involved all the commanding officers and staff sections of the entire army, aimed at preparing them for an all-out war with the South, KCNA reported.

The drill simulated repelling a sudden invasion, then launching a counter-attack to occupy "the whole territory of the southern half", the report said.