North Korea has been upgrading a missile launch site on its east coast in preparation for a test launch of a new long-range missile, a news report said Thursday.

South Korea's Dong-A Ilbo newspaper, citing intelligence sources, said activities at Musudan-ri on the coast of North Hamkyong province are focussed on upgrading the site with new equipment or building new facilities.

Intelligence authorities believe this indicates the North is preparing to test-fire a new long-range ballistic missile, an advanced model of the Taepodong-2 which can theoretically hit the US west coast, Dong-A said.

The North alarmed its neighbours by test-launching a Taepodong-1 from Musudan-ri in 1998 over Japan. It test-launched a Taepodong-2 from the same missile site in 2006 but the missile failed.

North Korea has replaced a tower on the launch pad and reinforced missile supports, it quoted an intelligence source as saying. It was also reportedly expanding facilities for assembling missile parts and for inspections.

Dong-A, quoting other sources, said the North is developing a new solid fuel-propelled ballistic missile, a modified model of the Taepodong-2 with a range of 10,000 kilometres (6,200 miles).

The current Taepodong-2 is said to have a range of 6,700 kilometres. The North has replaced its second-stage booster with a new engine, the paper said.

The South Korean defence ministry said it would not comment on military intelligence matters. The National Intelligence Service also declined comment.

Last month Chosun Ilbo newspaper reported that an ignition test for a Taepodong-2 missile had been carried out at a new long-range missile base under construction at Tongchang-ri on the west coast.

A six-nation nuclear disarmament deal is close to a breakdown. Some analysts believe the North may stage a missile launch or even a second nuclear test to put pressure on negotiating partners.

On Wednesday Yonhap news agency said increased activity had been spotted near the site of North Korea's 2006 nuclear test, but it was unclear whether the country is preparing for a second test.