North Korean leader Kim Jong Un ordered the production of more solid-fuel rocket engines and rocket warhead tips, the North's official media said on Wednesday in a report otherwise lacking threats against Washington after weeks of heightened tension.
US President Donald Trump also expressed cautious optimism about a possible improvement in relations with the North, after months of mounting tension over its weapons programmes.
Kim was briefed about the process of manufacturing intercontinental ballistic missile warhead tips and solid-fuel rocket engines during his tour of the Chemical Material Institute of the Academy of Defence Science, the North's official KCNA news agency said.
North Korea has conducted two nuclear tests and dozens of missile tests since the start of last year, significantly raising tensions on the heavily militarised Korean peninsula. Two tests of intercontinental ballistic missiles in July resulted in a new round of tougher global sanctions.
The last missile test on 28 July put the US mainland in range, prompting heated exchanges that raised fears of a new conflict on the peninsula.
Tillerson, however, noted what he called the restraint the North had shown lately and said on Tuesday he hoped a path could be opening for dialogue some time in the near future.
South Korea and the United States are conducting an annual joint drill involving computer simulations of a possible war on the Korean peninsula, exercises that the North routinely describes as preparation for invasion. The drills started on Monday and will run through to 31 August.
South Korea will also conduct a voluntary civil defence drill across the country later on Wednesday.
However, there was none of the fiery rhetoric of recent weeks, when Kim threatened to fire missiles into the sea near the US Pacific territory of Guam after US President Donald Trump earlier warned North Korea it would face "fire and fury" if it threatened the United States.
New US sanctions announced on Tuesday target Chinese and Russian firms, as well as individuals, for supporting Pyongyang's weapons nuclear and missile programmes.
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