Senior South Korean and US defence officials met in Seoul on Wednesday for talks focused on responding to the possibility of an imminent North Korean rocket launch and later nuclear test.

The two-day talks follow statements earlier this month by the respective heads of the North's space and atomic energy agencies that fuelled concerns over its nuclear and ballistic missile programmes.

There has been widespread speculation that Pyongyang may carry out a satellite rocket launch to mark the 70th anniversary of the ruling Workers Party on October 10.

The North insists its space programme is purely scientific, but the US, South Korea and their allies deem any such rocket launch to be a disguised ballistic missile test that violates UN resolutions.

Although there have been no physical signs of North Korea preparing a launch, the director of its space agency said the world would soon see "a series of satellites... soaring into the sky."

A day later, the head of the national atomic agency said the North's main nuclear weapons complex was fully operational -- including a uranium enrichment plant and a five-megawatt reactor seen as the country's main source of weapons-grade plutonium.

Opening Wednesday's talks in Seoul, Seoul's deputy minister for policy at the defence ministry, Yoo Jeh-Seung, said the meeting would seek to "firm up the combined defence posture" of South Korea and the United States.

"(This) carries special importance when North Korea's nuclear and missile threats are growing," he was quoted as saying by the Yonhap news agency.

The White House has already warned Pyongyang to refrain from any "irresponsible provocation" that might aggravate regional tensions.

The US officials at the talks included Abraham Denmark, deputy assistant secretary of defense for East Asia, and Elaine Bunn, deputy assistant secretary of defense for nuclear and missile defense policy.

The chief US envoy to the six-party talks on ending North Korea's nuclear weapons programme arrived in South Korea Tuesday and was expected to join the discussions.

The North's only successful satellite launch was of its Unha-3 rocket in December 2012 -- a move that resulted in UN sanctions and a surge in military tensions that culminated two months later in the North's third nuclear test.

The Unha-3 is seen as a prototype intercontinental ballistic missile (ICBM), although the North has yet to conduct a test showing it has mastered the re-entry technology required for an effective ICBM capability.

Developing a working ICBM would be seen as a game-changer, bringing the mainland United States within range of a possible nuclear strike.