SEOUL — North Korea’s leader Kim Jong-Un has ordered more production of rocket engines and intercontinental ballistic missile (ICBM) nosecones, Pyongyang state media said on Wednesday.

Tensions over the North’s weapons programmes have mounted this year and it carried out two ICBM tests last month, overseen by Kim, that apparently brought most of the United States within range.

A series of threats followed from both sides, and while the rhetoric has since eased, the US and South Korea this week kicked off their annual Ulchi Freedom Guardian military drills, which the North always condemns as dress rehearsals for invasion.

Kim inspected the Chemical Material Institute of the Academy of Defence Science, which develops the North’s missiles, KCNA reported on Wednesday.

"He instructed the institute to produce more solid-fuel rocket engines and rocket warhead tips," it said.

Questions remain whether the North has mastered the technology needed to ensure a ballistic missile warhead survives the intense heat generated by re-entering the Earth’s atmosphere, although it says it has done so.

The manufacturing process included carbon fibre weaving, chemical deposition and high pressure liquid deposition, KCNA said.

The North has threatened to fire a salvo of missiles toward the US Pacific territory of Guam, but has since backed away from the plan.

US Secretary of State Rex Tillerson on Tuesday added momentum to tension reduction, praising the North for showing a "level of restraint" in not conducting nuclear or missile tests since new UN sanctions were imposed.

He also expressed hope that it was a sign of Pyongyang’s readiness to enter peace and disarmament talks with Washington "sometime in the near future." — AFP