North Korea said Wednesday it test-fired ballistic rockets as part of a simulated pre-emptive attack on ports and airfields in South Korea, in a likely reference to the three missile launches that Seoul says the North carried out a day earlier. 
On Tuesday, Pyongyang test-fired three ballistic missiles, two Scuds and one Rodong, in an apparent "armed protest" against South Korea's recent decision to deploy an advanced US anti-missile system in the country to counter growing threats from the North. 
"The drill was conducted by limiting the firing range under the simulated conditions of making pre-emptive strikes at ports and airfields in the operational theater in South Korea, where the US imperialists nuclear war hardware is to be hurled," North Korea said in an English dispatch carried by the Korean Central News Agency (KCNA). 
North Korean leader Kim Jong-un "provided field guidance to the drill," observing that the ballistic missiles launched in Hwangju, North Hwanghae Province, flew across the country and hit the East Sea, the KCNA said. 
In the "successful" drill, the KCNA said North Korea "once again examined the operational features of the detonating devices of nuclear warheads mounted on the ballistic rockets at the designated altitude over the target area". 
On July 8, Seoul and Washington announced a decision to deploy the Terminal High-Altitude Area Defense (THAAD) system in South Korea by the end of 2017 to deal with evolving nuclear and missile threats from the communist country.

Source ; QNA