North Korean leader Kim Jong-un has vowed not to use nuclear weapons first unless the country's sovereignty is infringed upon in his speech at the key party congress, the country's state media said Sunday.

At the first congress of the Workers' Party of Korea (WPK) in 36 years, the North's leader said that Pyongyang is open to efforts to improve its ties with "hostile" countries. He also offered to hold military talks with South Korea to ease tension.

"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 (KCNA). "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, the duration of which is not known, 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 2016, in defiance of international condemnation and sanctions.

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 congress and followed up with numerous accomplishments made by the ruling party on Saturday.

Experts said that the leader's message reaffirmed his pursuit of his signature policy of developing nuclear weapons in tandem with boosting the country's moribund economy, commonly known as the "byeongjin" policy.

A Seoul government official said that Kim's remarks appear to mean that North Korea has no intent of giving up nuclear weapons.

"It seems that there has been no change in the North's stance that the country should be recognized as a nuclear state," the official, asking not to be named.

Touching on external relations, the North's leader said his country is ready to "improve and normalize" its ties with what the North calls hostile forces -- the United States -- when conditions are met.

"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 1950-53 Korean War that ended with only a ceasefire armistice.

On inter-Korean relations, Kim offered to hold military talks between the two rival Koreas in a bid to ease military tension on the peninsula.

Relations between South and North Korea had a short-lived reconciliation last year following their rare deal aimed at reducing military tension on Aug. 25. But their ties have become severely strained since the North's nuclear and missile provocations early this year.

"We see the need to have dialogue and talks between the two Koreas' military officials," he said. "If military talks are held, they would help eliminate risks of conflict along the border and ease tension."

But the South Korean government rejected the North's dialogue offer as a sheer propaganda ploy that lacks sincerity, calling on Pyongyang to give up its nuclear weapons program.

"The North's proposal is merely its propaganda drive with no sincerity as it speaks of inter-Korean dialogue while continuing to develop a nuclear arsenal," Seoul's unification ministry said in a statement.

The North's leader also stressed the need for a self-reliant unification, highlighting his predecessors' vision for unification.

At the congress held 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)