North Korea has claimed it has an invincible army and has warned it is waiting for an order to wage what it calls a final sacred war.

The strike, the state says, will turn into a sea of fire and destroy what it described as bluffing US imperialists.

The comments were made in Friday's Rodong Sinmun newspaper, which is the official media outlet for the Central Committee of the Workers' Party of Korea, led by Kim Jong-Un.

North Korean leader Kim Jong-Un (right) claps as he attends the unveiling ceremony of two statues of former leaders Kim Il-Sung and Kim Jong-Il in Pyongyang

The article, translated by KNCA Watch, told its North Korean readers the country's army was an 'invincible army equipped with powerful strike means and ever-victorious tactics.

It held a special mention for Donald Trump's administration, saying, 'the US imperialists are trying hard to attain its purpose through military threat and blackmail while brandishing all sorts of strategic and tactical weapons of demonstrative and threatening nature'.

'But it is nothing but a bluffing of the mentally weak and a last-ditch effort of those with miserable end at hand,' it added.

'The army of the Democratic People's Republic of Korea (DPRK), full of the spirit of annihilating the enemies, is waiting for an order to wage a final sacred war, with their guns leveled at the detestable targets.

'Our strike will all at once turn into sea of fire, completely destroying enemies and winning a final victory.'

Kim Jong-Un (front L) inspecting the command of Korean People's Army (KPA

The article insisted the words were not empty threats, and called the DPRK's stance on defence was an 'everlasting treasure'.

North Korea maintains that it must develop nuclear weapons because of the 'hostile' policy of the United States, which retains 28,500 troops in South Korea and holds bi-annual military drills the North considers rehearsals for invasion.

Tensions have spiked as President Donald Trump deployed an aircraft carrier strike group to waters off the Korean Peninsula.

Last week, North Korean Defense Minister General Pak Yong Sik said his country was ready to use pre-emptive strikes to defend against 'US imperialists,' warning nuclear war could break out because of the 'frantic war drills'.

Kim's Korea has provoked the periodic military clashes that break out with South Korea, and has ramped up its nuclear programme recently with a number of missile tests.

In March 2010, a North Korean torpedo allegedly sank a South Korean naval vessel, killing 46 sailors.

Months later, North Korea fired artillery at a South Korean island, killing two South Korean marines and two civilians.

South Korea returned fire, but it's unclear if North Korea suffered casualties.

North Korea is the only country to have conducted a nuclear explosion in the 21st century and it has accelerated weapons testing as aid-for-disarmament negotiations have stalled.

Between 1994 and 2008, it carried out 16 ballistic missile tests and one nuclear test.

Since 2009, 72 missile tests and four nuclear tests.

Even China, which fought on its side in the Korean War, opposes the testing, which violates UN Security Council resolutions. Experts say North Korea may already be able to hit South Korea or Japan with a nuclear weapon, and within years could have the capability to target the American mainland.

The article in the state newspaper said the North Korean army was invincible and ready for war

The words were penned just days before North Korea said it has detained another American citizen for suspicion of acts against the state.

It was confirmed by the state on Sunday, and made him the fourth US citizen to be held by the isolated country amid diplomatic tensions.

Kim Hak Song, who was detained on May 6, worked for the Pyongyang University of Science and Technology, the North's KCNA news agency said.

A third U.S. citizen, Kim Sang Dok, was detained in late April for hostile acts, according to the North's official media.