(ATTN: UPDATES with more details in last 4 paras)
By Lee Haye-ah
SEOUL, May 25 (Yonhap) -- North Korea has been testing a nuclear triggering device apparently in preparation for what would be the country's seventh nuclear test, a senior presidential official said Wednesday.
The experiments have been taking place at a location away from Punggye-ri, the site of all six North Korean nuclear tests to date, said Kim Tae-hyo, first deputy director of the National Security Office, without naming the place.
"Operation tests of a nuclear detonation device, which are to prepare for the seventh nuclear test at Punggye-ri, are being detected," Kim told reporters. "The possibility of an imminent nuclear test in the next day or two is low, but after that, there is certainly a possibility."
The last time North Korea carried out a nuclear test was in September 2017, when it claimed to have tested a hydrogen bomb.
The next few years saw the United States engage in unprecedented summit-level diplomacy to try to get the North to abandon its nuclear and missile programs, but the effort ultimately failed.
This year the North has launched missiles on 17 separate occasions, the latest of which came early Wednesday as U.S. President Joe Biden was en route to Washington after a five-day visit to South Korea and Japan.
Kim said he could not predict when the nuclear test would take place.
"It's likely the North Korean leader has not decided himself," he said. "The North Korean authorities are imminently near the final preparation stage for a nuclear test of a scale and quality they want."
Kim confirmed earlier assessments that Wednesday's launch involved one intercontinental ballistic missile of the newest Hwasong-17 model and two short-range ballistic missiles.
He suggested the SRBMs should not be dismissed as their launches were likely intended to improve their nuclear delivery capability.
He also claimed there was a political motivation behind the test-firings, such as to "interfere in the imminent domestic political schedule in the Republic of Korea," a likely reference to the upcoming June 1 local elections, and to "test the new government's security posture."
"The fact that they began the provocations around the time that U.S. President Joe Biden was entering his country's airspace was a strategic message to both South Korea and the United States," Kim said.
Later in the day, South Korea's spy agency told lawmakers that the launch was the first time North Korea had fired more than two types of ballistic missiles at the same time under the leadership of Kim Jong-un.
The National Intelligence Service (NIS) said in a closed-door briefing on North Korea that it is closely monitoring of the situation as there is a possibility that the North could carry out additional provocations, including a nuclear test, according to lawmakers.
"In its firing of ballistic missiles, North Korea appears to be testing various nuclear delivery means," Rep. Kim Byung-kee of the main opposition Democratic Party, told reporters after the briefing.
He said the NIS reported that the North's testing of a nuclear detonation device may not necessarily be a sign that its seventh nuclear test is imminent, as previous similar tests did not lead to a nuclear test.