SEOUL (Reuters) -North Korean leader Kim Jong Un said the country should be ready to conduct nuclear attacks at any time to deter war, accusing the U.S. and South Korea of expanding joint military drills involving American nuclear assets, state media KCNA said on Monday.

Kim’s remarks came as the isolated country conducted what KCNA called nuclear tactical exercises meant to send strong warnings against the allies.

In the exercises, a ballistic missile flew 800 km (497 miles) before hitting target at the altitude of 800 m (0.5 mile) under the scenario of a tactical nuclear attack, KCNA said.