SEOUL (AFP) - North Korea on Sunday vowed tough action against the United States, accusing it of plotting to blow up statues of its founding leader in a bid to stir turmoil in the isolated communist state.

The warning comes just days after the North said it would “completely review” the nuclear issue, amid concerns that Pyongyang may be planning a third nuclear test following its failed rocket launch in April.

Pyongyang has recently increased hostility towards Seoul and Washington, accusing them of sending a spy to the country with a mission to blow up statues of Kim Il-Sung, adding that the plot amounted to a “war action”. “(North Korea) has various types of strike means... powerful enough to render the US modern war means ineffective,” the country’s National Defence Commission said in a statement carried by the state-run KCNA news agency.

It vowed to launch a “powerful physical counter-offensive” against the United States, but did not elaborate on what that meant. The threat comes after the North arrested a man who was allegedly trying to blow up a monument to Kim Il-Sung.

Jon Yong-Chol was presented at a press conference in Pyongyang earlier this month, where he claimed he had been promised handsome rewards from Seoul intelligence agents if he succeeded in his mission.

The impoverished but nuclear-armed North has a pervasive personality cult surrounding its ruling family and has built numerous monuments for its late founding leader Kim Il-Sung who died in 1994 and his son Kim Jong-Il. In April two giant statues of the two late rulers were unveiled in the capital Pyongyang, just hours after the North’s failed rocket launch seen by the US and its allies as an attempted ballistic missile test.

Meanwhile, North Korea warned the South not to expect any major reforms under the leadership of Kim Jong-Un, with a senior official rejecting discussion of potential policy change as a “foolish and silly dream”.

Kim, believed to be in his late 20s, took the reins of power in December following the death of his father, longtime ruler Kim Jong-Il. Speculation of impending change was fuelled earlier this month when the communist regime sacked prominent military chief Ri Yong-ho and replaced him with a little known general and promoted Jong-Un to the top military post of Marshal.

The secretive nation also made a rare announcement last week that the young ruler is married, in a major departure from the past when the private lives of his predecessors were kept under wraps.

Seoul commentators claimed the changes may have been implemented to set the stage for possible efforts by Swiss-educated Kim to open up the country to political or economic reforms. But a spokesman for the North’s Committee for the Peaceful Reunification of Korea, which is in charge of cross-border affairs, blasted such hopes as “ridiculous” and “ignorant” in an interview with state-run KCNA on Sunday.

“The puppet group (the South)... tried to give (the) impression that the present leadership of the DPRK (North Korea) broke with the past. This is the height of ignorance,” he said. “To expect policy change and reform and opening from the DPRK is nothing but a foolish and silly dream, just like wanting the sun to rise in the west.”

He also accused Seoul of trying to impose its capitalist system upon the North by “trumpeting reform and opening”, adding, “there cannot be any slightest change in all policies” of the communist state.

Kim inherited from his father an economy in ruins after decades of mismanagement, and a malnourished population dependent on foreign food aid.

Educated in the West, he has been seen as potentially more receptive than his father to undertaking sweeping reforms which would open up the nation’s crumbling economy.

However, the International Crisis Group (ICG) thinktank said last week that there was nothing to suggest that Kim would take measures to improve the lot of his impoverished people in the isolated state.

The Brussels-based ICG said that economic reform — however necessary to the country’s wellbeing — would contradict the centrally-planned system espoused by Kim’s father and grandfather.

Inter-Korea ties have been particularly icy since the South’s conservative leader Lee Myung-Bak took office in 2008, repeatedly urging the North to reform and saying reunification was imminent, despite complaints from Pyongyang.