By Jack Kim

SEOUL, March 4 (Reuters) - A North Korean missile launch may not come for some time although the communist state has been preparing its longest-range rocket for a test flight, South Korea's unification minister said on Wednesday.

North Korea has raised regional tensions in recent weeks by threatening to attack the South and preparing its longest-range Taepodong-2 missile for a launch. The missile is designed to carry a weapon as far as Alaska, but has never successfully flown.

"I don't believe a missile launch is quite imminent, but there are preparations ongoing," Unification Minister Hyun In-taek told reporters.

The North has said it is preparing to launch a satellite and has the right to do so as part of its peaceful space programme. The North is barred from test-firing its ballistic missiles under U.N. sanctions.

Hyun did not say what he based his assessment on, but South Korean officials have said the country receives photographs of sensitive sites in the North from U.S. spy satellites and has its own intelligence on the North.

Analysts have said the North may be looking to launch the missile as soon as next week to mark an election for members of its rubber-stamp parliament. Another possible date is April 25, the anniversary of its Korea People's Army.

The United States has sent Stephen Bosworth, its new special envoy for North Korea, to the region this week in a bid to advance floundering talks on ending the North's nuclear weapons programme and to prevent Pyongyang from making provocative moves.

Bosworth started his trip in Beijing on Tuesday and had "substantive and detailed" talks with Chinese Vice Foreign Minister Wu Dawei about how to proceed, a U.S. State Department spokesman told reporters in Washington.

Bosworth, a former U.S. ambassador to South Korea, will also travel to Tokyo and Seoul.

Six-way talks on ending the North's atomic ambitions have stalled over North Korea's refusal to agree to a system to check its nuclear programme, as demanded by the other parties. The North has complained that aid is not being delivered as promised. (Writing by Jon Herskovitz; Editing by Jonathan Hopfner)

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