North Korea is said to be working on an advanced version of its intercontinental ballistic missile(ICBM) that could potentially reach the U.S. mainland.
 
In a report published Thursday, U.S. officials told CNN that the North is working on an advanced version of its KN-20 ICBM as part of efforts to improve every part of its missile and nuclear weapons attack capabilities as quickly as possible.
 
The North is also said to be working on improving its nuclear fuel, missile launchers, and guidance and targeting systems.
 
CNN said the North’s continued development of its nuclear weapons and missile programs are forcing the U.S. to reassess how soon North Korea’s threat could become a reality.