North Korean leader Kim Jong-un is claiming that his country has developed a hydrogen bomb, which produces a more powerful nuclear explosion than an atom bomb.
However, international experts say this could not be confirmed.
An H-bomb, also known as thermonuclear bomb, uses more advanced technology to produce a significantly more powerful blast than an atomic bomb, reports say.
The North Korean leader made the remarks while on a tour of the Phyongchon Revolutionary Site as he commemorated the achievements of his father Kim Jong-il and his grandfather, Kim Il-sung, on Thursday, South Korean state news agency Yonhap reported.
The work of his granddad "turned the DPRK into a powerful nuclear weapons state ready to detonate a self-reliant A-bomb and H-bomb to reliably defend its sovereignty and the dignity of the nation," Kim Jong-un was quoted as saying.
State media reported that that was the first time the North Korean leader announced publicly that the country had developed a hydrogen bomb.
Experts, however, said the claims made by Kim are extremely difficult to confirm since North Korea is a very secretive nation.
An official at South Korea's intelligence agency told Yonhap news agency there was no evidence that the north had hydrogen bomb capacity, and said he believed Kim was speaking ''rhetorically,'' the Independent reported.
"It's hard to regard North Korea as possessing an H-bomb. I think it seems to be developing it,'' said Lee Chun-geun, a Science and Technology Policy Institute research fellow.
Jeffrey Lewis of the California-based Middlebury Institute of International Studies at Monterey also felt the same way. "I think it is unlikely that they have H-bomb at the moment, but Ii don't expect them to keep testing basic devices indefinitely, either,'' he said.
"It was possible that the North was referring to the technology of boosting the yield of a nuclear device, possibly using fusion fuel,'' Lewis said, the Guardian reported.
North Korea conducted underground tests to set off nuclear devices in 2006, 2009 and 2013, for which it has been subjected to U.N. Security Council sanctions banning trade and financing activities that aid its weapons programme, reports said.
Asked about Kim's remarks, Hua Chunying, spokeswoman for the Foreign Ministry of China, told a daily news that Beijing is dedicated to ensuring the denuclearisation of the Korean peninsula and resolving problems through talks.
China is North Korea's most important economic and diplomatic backer.
In a speech to mark the 70th anniversary of the founding of the ruling communist Workers' Party on Oct. 10, Kim said he is prepared to wage war against South Korea and its major ally, the United States.
