An Indonesian delegation led by Coordinating Human Development and Cultural Affairs Minister Puan Maharani delivered a personal invitation to Kim during their visit to North Korea this week.
The North Korea flag flutters next to concertina wire at the North Korean embassy in Kuala Lumpur, Malaysia, March 2017.
Reuters also added that satellite imaging showed vehicles moving in and out of the facility, but not the extent of any missile construction.
"What's more, a liquid-fuelled ICBM doesn't pose nearly the threat that a solid-fuelled one would because they take so long to fuel, and that's something we almost certainly could see in time to abort a launch, given our assets in the vicinity".
Her comments come after a report this week in The Washington Post that United States intelligence officials had discovered fresh evidence that the North was building new ICBMs.
USA spy satellites have detected renewed activity at the North Korean factory that produced the country's first intercontinental ballistic missiles capable of reaching the United States, a senior U.S. official said on Monday, in the midst of talks to compel Pyongyang to give up its nuclear arms.
A United States official having knowledge of the latest intelligence assessment on Pyongyang told Fox News, "It's business is as usual".
But at the Sohae Satellite Launching Station on North Korea's west coast, workers can be seen dismantling an engine test stand, in line with a promise made to Trump at the summit, though the move is seen as more symbolic since the facility can easily be rebuilt.
President Trump 'Open to Visiting Moscow' If Putin Formally Invites Him
Mr Putin said on Friday: "I understand very well what President Trump said: He has the wish to conduct further meetings. Both Trump and Putin have said they are determined to improve relations.
A bright-red covered trailer, identical to the those the country used to transport previous ICBMs, was photographed on July 7 at the facility's loading area.
Reports had indicated that North Korea was upgrading its only official nuclear enrichment site, and was stepping up enrichment at other secret sites.
Late last month, the Post reported that new intelligence gathered after the summit suggest North Korea's real plan was to simply lie about denuclearization and hold on to its nukes.
Meanwhile, generals from the two Koreas have met at the border village of Panmunjom for talks about implementation of agreements on non-nuclear military issues reached at April's inter-Korean summit.
"Regime survival and perpetuation of Kim family rule" are Kim's guiding principles, he said.
But the actual details of the process, including how and when the North's nuclear programme is to be dismantled, have yet to be worked out.
"I'm afraid that at this point, the United States, the Trump Administration is being taken for a ride", said Sen.
Fissile material refers to either uranium highly enriched in the uranium-235 isotope or plutonium-239, both of which are suitable for use in nuclear weapons. What they're offering is: "They keep the bomb, but they stop talking about it".