Three hawkish generals in North Korea's all-powerful army pushed leader Kim Jong-Il into conducting his declared nuclear test, a leading analyst said on Monday.
Other analysts also saw the hand of the 1.2 million-strong military as being behind the announcement, which shocked the world and prompted UN sanctions.
Nam Sung-Wook, a North Korea expert and professor at Korea University, identified Pak Jae-Gyong, Hyon Chol-Hae and Lee Myong-Su as the key drivers of Kim's brinkmanship.
"The trio, accompanying Kim like shadows, were definitely behind the decision to push ahead with the nuclear test," he told AFP.
Nam said Pak and Hyon are deputy chiefs of the politburo of the Korean People's Army (KPA) and Lee is its deputy operations bureau chief.
The North's official statement announcing the test clearly showed it was designed to please the military, which under a Songun (army-first) policy gets the best of everything in the impoverished state.
"It (the test) marks a historic event as it greatly encouraged and pleased the KPA and people that have wished to have powerful self-reliant defence capability," read the statement.
Koh Yu-Hwan, another North Korean expert and professor at Dongkuk University, said "only a handful of people" must have been involved in the test but admitted difficulty in pinpointing who they were.
"Kim, holding absolute power up there, seemed to side with the hardline military rationale that if North Korea conceded to US pressure once, it would keep conceding," Koh said.
"The North Korean leader may have had difficulty denying his own-created Songun policy in the face of pressure from hardliners."
The United States had increased pressure on North Korea to frustrate its nuclear ambitions but this served as justification for Kim to side with the hardliners, Koh said.
"The ultra-strong measure was taken according to Kim's belief that the US pressure had already become unendurable."
Koh forecast that the North's diplomats, who advocate negotiation, would have little room to manoeuvre for the time being due to the hardliners.
One measure said to have especially hurt the leadership was US financial sanctions on a Macau bank accused of laundering money from counterfeiting and other illegal activities.
North Korea has refused to return to six-party disarmament talks unless the United States lifts the sanctions.
Hong Kong-based security consultancy International Risk said in a report last week that Kim would not easily collapse, having "made strenuous efforts to build up his power base within the military."
It said the military had been well-fed and well-equipped despite general economic hardship in North Korea since the end of the Cold War, with a drastic cut-off in economic assistance from the former communist bloc.
The consultancy said that while interactions with the world in recent years have ostensibly been handled by Kim and the country's diplomats, "the hardline policy approach that Pyongyang took shows the heavy hand of the generals who have been opposed to negotiating away the country's nuclear weapons capability."