SEOUL (AFP) - North Korea has now moved two intermediate range missiles to its east coast and loaded them on mobile launchers, South Korea's Yonhap news agency said on Friday, citing a top government official.

The Defence Ministry, which had confirmed the movement of one missile the day before, declined to comment on the new report.

"It has been confirmed that North Korea, early this week, transported two Musudan mid-range missiles by train to the east coast and loaded them on vehicles equipped with launch pads," Yonhap quoted the official as saying.

It marks the latest incremental move by North Korea which, incensed at fresh UN sanctions and South Korea-US military drills, has issued a series of apocalyptic warnings of nuclear war in recent weeks.

The United States said on Thursday it was taking "all necessary precautions" against the threats emanating from Pyongyang.

The government official said the vehicles carrying the missiles had apparently been hidden in special underground facilities.

"The North is apparently intent on firing the missiles without prior warning," he added.

The Musudan has never been tested, but is believed to have a range of around 3,000km, which could theoretically be pushed to 4,000 with a light payload.

That would cover any target in South Korea and Japan, and possibly even reach US military bases located on the Pacific island of Guam.