Donald Trump has insisted North Korea will not develop a nuclear weapon capable of reaching the US.

The President-elect addressed the issue on Monday evening on Twitter. North Korean leader Kim Jong-un had hinted that his country would test an intercontinental ballistic missile in the new year.

Mr Trump tweeted: "North Korea just stated that it is in the final stages of developing a nuclear weapon capable of reaching parts of the U.S. It won't happen!"

It was unclear if Trump meant he would stop North Korea or he was simply doubting the country's capabilities. His aides did not immediately respond to questions seeking clarification.

Also on Twitter, Mr Trump then berated North Korea's most important ally, tweeting: "China has been taking out massive amounts of money & wealth from the U.S. in totally one-sided trade, but won't help with North Korea. Nice!"

Kim said in his annual New Year's address that preparations for launching an ICBM have "reached the final stage", He did not explicitly say a test was imminent.

Earlier on Monday, experts said North Korea's claims regarding an ICBM were plausible. They said the isolated state had testing rocket engines and heat-shields for such a missile while developing the technology to guide an ICBM after re-entry into the atmosphere following lift-off.

While Pyongyang is close to a test, it is likely to take some years to perfect the weapon.

Once fully developed, a North Korean ICBM could threaten the continental United States, which is around 9,000 km (5,500 miles) from the North. ICBMs have a minimum range of about 5,500 km (3,400 miles), but some are designed to travel 10,000 km (6,200 miles) or further.

North Korea's state media regularly threatens the United States with a nuclear strike, but before 2016 Pyongyang had been assumed to be a long way from being capable of doing so.

"The bottom line is Pyongyang is much further along in their missile development than most people realise," said Melissa Hanham, a senior research associate at the U.S.-based Middlebury Institute of International Studies at Monterey, California.