"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," Kim was quoted as saying by the Korean Central News Agency. "It will faithfully fulfill its obligation for non-proliferation and strive for global denuclearization."

His remarks came on the second day of the WPK's party congress, which kicked off its first session in more than three decades on Friday.

The political event, which may last for up to four days, is widely expected to reaffirm Kim's monolithic power and highlight the leader's future goals for the country.

The event is being held amid growing speculation that North Korea could carry out its fifth nuclear test at any time. North Korea conducted a nuke test in January and launched a long-range rocket the following month, prompting the U.N. to impose its strongest ever sanctions on North Korea.

The reclusive country detonated its first nuclear device in

2006 and followed up with other tests in 2009, 2013 and in January of this year, all in defiance of calls by the international community.

The North's leader trumpeted the country's nuclear test and long-range rocket launch early this year when he delivered an opening speech on the first day of the party congress and followed up with numerous accomplishments made by the ruling party on Saturday.

Touching on external relations, the North's leader said his country is open to improving its ties with what the North calls hostile forces -- the United States.

"The WPK and the DPRK government will improve and normalize 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 said.

The DPRK stands for the Democratic People's Republic of Korea, the North's official name.

Pyongyang has consistently demanded that U.S. troops stationed in South Korea leave the peninsula. It has also called for signing a peace treaty to officially end the Korean War (1950-53) that ended with only a ceasefire armistice.

On inter-Korean relations, Kim stressed the need for a self-reliant unification, highlighting his predecessors' vision for unification.

At the congress in 1980, North Korea's founder Kim Il-sung unveiled a blueprint for unification, claiming that the only realistic way to achieve unification is the federation system which calls for the respect of each other's differences in political ideology and government system.

"We should consistently keep a firm hold on the three charters for national reunification which comprehensively deal with the will and requirements of all Koreans," the North's leader said.

The concept of the charters for unification encompasses the July 4 Joint Communique issued by the two Koreas in 1972 as well as policy guidelines set by the North in 1980 and 1993.

The party gathering is the first of its kind since October 1980 and also the first under the current leader, who assumed power in late 2011 following the sudden death of his father Kim Jong-il. (Yonhap)