Pyongyang staged a simulated "tactical nuclear attack" drill on Saturday, the North Korean state news agency KCNA.
The exercise was a show of strength to "warn enemies" and let them know that the country is prepared in case of a nuclear war, the state news agency said on Sunday.
Mock warheads fired
As part of the drill, mock atomic warheads attached to two long-range missiles were testfired off the west coast of the country.
The "counteraction drill" was reportedly conducted in response to joint military activity by US and South Korean forces.
North Korean leader Kim Jong Un also visited the Pukjung Machine Complex, which manufactures marine engines and has a major munitions factory.
He inspected the shipbuilding and munitions factories to stress the importance of Pyongyang's naval forces, KCNA reported.
Kim also detailed future plans regarding the "modernization of the complex and the development direction of the shipbuilding industry," which was underway, a statement by the state news agency said.
Tensions on the rise
South Korea's joint chief of staff confirmed on Saturday that an unspecified number of cruise missiles were launched toward the Yellow Sea.
The latest drill came just after the 11-day joint annual summertime exercises between Washington and Seoul, known as Ulchi Freedom Shield concluded on Thursday.
Pyongyang said that the joint exercises reflected how the US and South Korea were pursuing "confrontation hysteria."
That statement came even as North Korea this year has conducted a record number of weapons tests.
UN resolutions prohibit isolated North Korea from launching and testing ballistic missiles of any range.
