The panel made the assessment in a new report for the UN Security Council committee monitoring sanctions implementation against North Korea, adding that the regime's nuclear weapons program also continues unabated.
The report covers the period Feb. 2 - Aug. 2, and comes as US-North Korea denuclearization negotiations have stalled since the no-deal summit between US President Donald Trump and North Korean leader Kim Jong-un in February, with the two sides apart on how far the North needs to denuclearize in exchange for sanctions relief from the US.
The experts in particular noted the significance of recent short-range ballistic missile tests by North Korea, which Trump has dismissed as "very standard."
The new class of SRBMs launched on May 4 and 9, as well as two missiles described by the North as a "new-type tactical guided weapon" launched on July 24, "are evidence of the DPRK's ability to master key components of ballistic missile systems, including solid rocket fuel production, mobility through the use of different types of transporter erector launcher (TEL) and the capacity to penetrate ballistic missile defense systems," according to the document.
DPRK stands for North Korea's official name, the Democratic People's Republic of Korea.
There is a "clear development progression from propellant for artillery rockets/SRBMs to solid propellant for ICBMs," the report says, adding that systems integration and internal synergies ensure that developments on the SRBM program benefit medium-range and intercontinental ballistic missile programs.
"With regard to missile engine development," the report says, "the DPRK's current goal appears to be to develop a solid-fueled first stage for its ICBM."
To further support their case, the experts note that regular activity has been observed at ICBM bases close to the northern border, including at the Hoejung-ri site, and that the North's priority is to secure the railway network supporting its ICBM brigades.
North Korea twice tested an ICBM in 2017, posing a threat to the American mainland. Trump has since boasted that Kim's suspension of nuclear and ICBM tests resulted from his diplomatic engagement with the regime.
But the report notes that the North's "nuclear program continues to operate despite the absence of nuclear testing and the closure of the test site at Punggye-ri."
It also points to continued operations at the Yongbyon uranium enrichment facility and the uranium concentration complex and mining sites in Pyongsan.
Meanwhile, the rocket launch site in Dongchang-ri, which the North began to dismantle after Trump and Kim's first summit in June 2018, appears to have been restored.
"The vertical missile-engine test stand is now renovated and possibly operational," according to the report. (Yonhap)