* Kim Jong Un declares North Korea a nuclear power
* New Hwasong-15 missile can reach all U.S. - N.Korea
* Missile lands in Japan exclusive economic zone
* Russia and China both express concern
* For multimedia coverage of North Korea https://www.reuters.com/north-korea/
By Christine Kim and Phil Stewart
SEOUL/WASHINGTON, Nov 29 (Reuters) - North Korea said it successfully tested a new intercontinental ballistic missile on Wednesday in a 'breakthrough' that puts the U.S. mainland within range of its nuclear weapons whose warheads could withstand re-entry to the Earth's atmosphere.