South Korea and the United States have signed an upgraded operational plan that puts a fresh focus on removing North Korea's weapons of mass destruction, a military official said Thursday.

In June, the allies signed OPLAN 2015, which will be put into action in case a war breaks out on the Korean Peninsula, according to the official.

"The militaries of both countries drew up OPLAN 2015, which replaces OPLAN 5027, with their Joint Chiefs of Staff chairmen signing it in June," the official noted.

For the past decades, OPLAN 5027 and its variants had been addressing how South Korea and the U.S. would combine their forces in the event of war with North Korea.

The upgraded operations plan focuses on aggressively removing North Korea's WMDs, including nuclear bombs, missiles and biochemical weapons, as well as launching a pre-emptive attack if an emergency situation arises.

The new plan has been already put into practice, with the allied forces carrying out their on-going joint Ulchi Guardian Freedom exercise under the scheme.

"This year's UFG has put a major priority on minimizing damage in case the North uses biochemical weapons," another official said.

The allies appeared to suffer more casualties from North Korea's ballistic missile-launched biochemical weapons in this year's simulated exercise compared with last year's, the official said.

Other sources said details of OPLAN 2015 have yet to be laid down for each echelon in both countries' militaries. (Yonhap)