North Korea's ties with China, its main ally and economic benefactor, have been strained over Pyongyang's persistent pursuit of nuclear and missile programs. China has implemented U.N. sanctions on North Korea over its nuke and missile tests.

The North sent a congratulatory message to China over the 18th party congress, which was held in 2012. It vowed to defend and strengthen the friendly relationship between the two countries.

But this time, Pyongyang sent the three-sentence message without mentioning the future direction of their ties.

Some experts said that the North's delivery of a congratulatory message indicates party-to-party exchanges are being kept, despite icy ties between the two nations.

"The move seems to mean that North Korea has no intent to cut off its traditional ties with China's party," said Park Byung-kwang, senior research fellow at the state-run Institute for National Security Strategy.

Seoul's spy agency earlier said that North Korea could fire an intercontinental ballistic missile on a standard trajectory over the Pacific around the time of China's party event. However, officials say there are no clear signs of possible North Korean provocation.

Unification Minister Cho Myoung-gyon told a forum that it is fair to say that there is a low chance of North Korea giving up its nuclear weapons.

The minister dismissed as unrealistic calls by some politicians for the redeployment of Washington's tactical nuclear weapons to the Korean Peninsula.

"The government is currently not considering such a move. ... Redeployment of tactical nukes means that we would recognize North Korea as a nuclear state," Cho said. (Yonhap)