The North will faithfully fulfill its obligation for nuclear non-proliferation and strive for ending nuclear buildup in the world, Kim said in a report to a congress of its ruling Workers' Party (WPK) which opened on Friday, KCNA news agency said.
The first congress in 36 years began with much fanfare amid anticipation by the South Korean government and experts that the young leader will try to use it to further consolidate power in a state he took over in 2011 after his father's sudden death.
"As a responsible nuclear weapons state, our Republic will not use a nuclear weapon unless its sovereignty is encroached upon by any aggressive hostile forces with nukes," KCNA quoted Kim as saying.
"And it will faithfully fulfill its obligation for non-proliferation and strive for the global denuclearization."
"The WPK and the DPRK government will improve and normalise the relations with those countries which respect the sovereignty of the DPRK and are friendly towards it, though they had been hostile toward it in the past," Kim was quoted as saying.
DPRK is short for the North's official name, the Democratic People's Republic of Korea.
In a separate item earlier, KCNA said Kim made the comments on the second day of the meeting on Saturday.
Kim also called for improved ties with the rival South by erasing misunderstanding and mistrust, although he had made similar proposals in the past that led to talks by government officials that made little progress.
North Korea came under toughened new U.N. sanctions in March after its fourth nuclear test in January and the launch of a long-range rocket that put an object into space orbit in defiance of past Security Council resolutions.
Since then, it continued to engage in nuclear and missile development activities and claimed that it had succeeded in miniaturizing a nuclear warhead and launching a submarine-based ballistic missile.
Kim also added the isolated state should continue to build and launch satellites, which US and South Korea view as a disguised test for long-range missiles.
