North Korea is capable of producing a nuclear bomb every six or seven weeks, it has been reported.
The New York Times reported that the US government has commissioned a number of studies which show North Korea’s nuclear intent.
It said US president Donald Trump’s recent stance on North Korea was guided by intelligence reports pointing to such a short time-frame to launch a nuclear strike.
The report comes as a US submarine sent by Mr Trump arrived in South Korea.
The USS Michigan arrived at a naval base in Busan, and will join an incoming group of warships led by aircraft carrier Carl Vinson.
The New York Times reports that North Korea is threatening its sixth nuclear test in 11 years.
China has warned North Korea that it will ‘cross the point of no return’ if the test is carried out, according to a report in the state-controlled Chinese Global Times.
Meanwhile, North Korean leader Kim Jong-un is believed to have overseen major live-fire drills in the North Korean town of Wonsan to mark the 85th anniversary of the founding of its army.
Envoys from the US, Japan and South Korea have met in Tokyo to discuss the growing threat posed by North Korea’s nuclear weapons and missiles programme.
Experts fear North Korea might conduct a nuclear test or a ballistic missile launch to mark the anniversary.
Crowds in Pyongyang, the North Korean capital, laid flowers and paid respects at giant statues of the country’s former leaders Kim Il-sung and Kim Jong-il, one day after the minister of defence reiterated that the North was ready to use pre-emptive strikes or any measures it deems necessary to defend itself against ’US imperialists’.
Gen Pak Yong-sik told a meeting of thousands of senior military and civilian officials: ‘The situation prevailing on the Korean Peninsula is so tense that a nuclear war may break out due to the frantic war drills of the US imperialists and their vassal forces for aggression.’
South Korea’s Joint Chiefs of Staff said they are closely watching North Korean military action in the Wonsan city area, where the drills are reportedly being held.
South Korea’s Yonhap news agency said the exercise involved 300 to 400 artillery pieces, but an official from Seoul’s defence ministry could not confirm these details.
The USS Michigan, a nuclear-powered submarine, arrived at the South Korean port of Busan in what was described as a routine visit to rest the crew and load supplies. Cmdr Jang Wook from South Korean navy public affairs said there is no plan for a drill.
The submarine’s arrival comes as the USS Carl Vinson aircraft carrier headed toward the Korean Peninsula for a joint exercise with South Korea.
The US 7th Fleet said two American destroyers are conducting simultaneous maritime exercises with naval ships from South Korea and Japan.
Despite the build-up, US president Donald Trump has reportedly settled on a strategy that emphasises increased pressure on North Korea with the help of China, the North’s only major ally, instead of military options or trying to overthrow the government in Pyongyang.
Mr Trump told ambassadors from UN Security Council member countries that they must be prepared to impose additional and stronger sanctions on North Korea.
He said: ‘This is a real threat to the world, whether we want to talk about it or not.
‘North Korea is a big world problem, and it’s a problem we have to finally solve. People have put blindfolds on for decades, and now it’s time to solve the problem.’