Washington, Nov 2 (IANS): North Korea is working on an advanced version of its existing KN-20 intercontinental ballistic missile that could potentially reach Washington, a US official told CNN CNN.

This newly assessed ICBM is just one part of an accelerated effort by Kim Jong-un's regime to improve every part of its missile and nuclear weapons attack capability as quickly as possible, the official said late Wednesday.

Additional new improvements are underway to North Korea's nuclear fuel, missile launchers, guidance and targeting systems as well, he added.

This development comes ahead of President Donald Trump's visit to Asia, where North Korea's nuclear programme will be a major topic of discussion.

North Korea also appears to have made critical progress in developing warheads that will be capable of re-entering the Earth's atmosphere and reaching a target at intercontinental ranges, CNN reported.

At least two recent ballistic missile tests demonstrated a dummy warhead successfully re-entering the atmosphere at least in a limited fashion, by not shattering.