North Korea may conduct another nuclear test or launch a long-range rocket ahead of its key party congress in May to maximize the impact of its provocations, experts said Wednesday.

North Korea said Tuesday it plans to carry out nuclear warheads and ballistic missiles tests "in a short time" in an apparent show of its defiance against tougher United Nations Security Council sanctions.

The North's threats have raised the possibility that Pyongyang may make more nuclear and missile provocations this year following its Jan. 6 nuclear test and long-range rocket launch on Feb. 7.

"Given its track record, North Korea is likely to make additional provocations to show that its nuclear capacity is not overblown and to strengthen internal solidarity," said Chung Sung-yoon, a researcher at the Korea Institute for National Unification.

The North usually ups the ante ahead of prominent political events or key anniversaries to maximize the impact of its belligerent acts and elicit allegiance from the general public.

One of the two upcoming key events for the North is the "Day of the Sun," which falls on April 15, the birthday of late founder Kim Il-sung, the grandfather of the current leader Kim Jong-un.

The ruling Workers' Party of Korea, meanwhile, plans to hold its first party congress in more than three decades in May. Seoul's spy agency said the party event is expected to be held on May 7.

"The North is likely to make provocations between late April and early May," Chung said, adding that it is more likely to conduct the fifth nuke test.

Others like Yang Moo-jin, a professor at the University of North Korean Studies, said that the North may launch an intermediate-range missile right before the party congress, rather than choose another nuclear test.

"It won't be easy for the North to carry out another nuke test as I think that Pyongyang would want to reserve it as a bargaining chip for possible talks with a new U.S. government," Yang said.

But experts also said that if the North does not make high-profile provocations before the party event, it may try to utilize its nuclear weapons as a card for dialogue.

The North detonated three nuclear devices in 2006, 2009 and 2013, and followed with a fourth test in January. (Yonhap)