North Korea's latest intercontinental ballistic missile, which it said could reach the "whole mainland" of the United States, broke up as it re-entered the Earth's atmosphere, a US official has said.

South Korea's military believes the Hwasong-15 missile, which flew 950km (600 miles) before splashing down in waters near Japan, is potentially capable of striking targets as far as 13,000km (8,100 miles), which would put Washington within reach.

But a US official told CNN "the North Koreans had problems with re-entry."

While North Korea's latest missile test puts Washington within range, Pyongyang still needs to prove it has mastered critical missile technology, such as re-entry, terminal stage guidance and warhead activation, South Korea said last week.

After North Korea released video footage and photographs of Hwasong-15, US based experts said it appeared North Korea was indeed capable of delivering a nuclear weapon anywhere in the US and could only be two or three tests away from being combat ready.

Yeo Suk-joo, South Korea's deputy minister of defence policy, told the South Korean parliament North Korea still needed to prove some technologies, like re-entry, terminal stage guidance and warhead activation.

North Korea announces test of new long-range missile

Mr Yeo said the first stage engine of the missile featured a clustering of two engines from a smaller Hwasong-14 ICBM test-launched in July.

North Korea announces intercontinental missile launch Show all 13 1 /13 North Korea announces intercontinental missile launch North Korea announces intercontinental missile launch Pyongyang residents react after the news of the successful launch of the new intercontinental ballistic missile AFP/Getty Images North Korea announces intercontinental missile launch North Korea's leader Kim Jong Un signing an order to test-fire the newly developed inter-continental ballistic missile KRT via AP Video North Korea announces intercontinental missile launch A news broadcast displays Kim Jong Un's signed document AP North Korea announces intercontinental missile launch People cheer as they watch the news broadcast announcing Kim Jong Un's order to test-fire the new inter-continental ballistic missile AFP/Getty Images North Korea announces intercontinental missile launch Residents react after the document signing AP North Korea announces intercontinental missile launch Pyongyang residents celebrate Kim Jong Un's announcement AFP/Getty North Korea announces intercontinental missile launch Cheering Pyongyang residents react AP North Korea announces intercontinental missile launch To counter North Korea's missile test, South Korea fired missiles into the East Sea The Defence Ministry/Yonhap via REUTERS North Korea announces intercontinental missile launch The Hyunmu-2 missiles firing during the drill South Korean Defense Ministry vi North Korea announces intercontinental missile launch The exercise was carried out in an attempt to counter Kim Jong Un's order South Korea Defense Ministry via AP North Korea announces intercontinental missile launch The South Korean army continue to carry out military exercises AP North Korea announces intercontinental missile launch Where K-9 self-propelled howitzers were taking part in a drill Rex Features North Korea announces intercontinental missile launch US soldiers are also present in the border city of Paju AFP/Getty Images

South Korea's Defence Minister, Song Young-moo, told parliament he expected North Korean leader Kim Jong-un to use his New Year's Address to declare North Korea had completed its weapons programme.

The dictator visited a factory which built the tires for a huge vehicle used to transport the new intercontinental ballistic missile to thank its workers.

At the factory, Kim complimented workers for manufacturing the large-size tires for the 9-axle missile truck without relying on imported equipment and called for efforts to raise production to "satisfy the daily-increasing needs in developing the country's economy and beefing up national defence capabilities," the North's official Korean Central News Agency said Saturday.

In September Kim tasked the Amnokgang Tire Factory to make the tires for the "great event in November," the agency reported.