A senior US official warned Tuesday that North Korea will face "strong actions" from the international community if it goes ahead with a long-range rocket launch in violation of UN resolutions.

"We hope they rethink that idea. But if they don't it's very clear there will be strong actions taken by the international community," US Deputy Secretary of State Tony Blinken told reporters after talks with South Korean officials.

"We are absolutely unified and in solidarity with regard to challenges posed by North Korea," he added.

There has been speculation for months that the North might launch a long-range rocket to celebrate the 70th anniversary of its ruling Workers' Party on Saturday.

But South Korean officials said North Korea showed no sign of preparing for a rocket launch.

"We don't see any signs of making preparations for an imminent launch such as the movement of a launch vehicle" to the launch pad, a Unification Ministry official said on condition of anonymity.

"After moving components of a launch vehicle, it usually takes two to four weeks of preparations to launch."

Remarks by the head of the North's space agency had fuelled conjecture about a launch to mark the anniversary. Comments by the chief of the North's national atomic commission led to additional talk of a possible fourth nuclear test.

Pyongyang insists its space programme is purely scientific and designed to put peaceful satellites in orbit. But Washington and its allies have warned that any rocket launch will be deemed a test of ballistic missile technology in violation of UN resolutions.

"There is no evidence to support a long-range rocket launch on October 10," Joel Wit, an expert at the US-Korea Institute at Johns Hopkins University, said on Twitter on Monday.

"North Korea could be doing things at night that we cannot watch via satellite, but most government officials agree that there will not be a launch," he said at #38NorthPress.

Citing satellite images of the North's Sohae Satellite Launching Station, the US-Korea Institute said last month on its closely watched website 38 North that a launch on or before October 10 was possible but unlikely.

Pyongyang successfully launched a three-stage, Unha-3 rocket carrying a satellite on December 12, 2012 from the Sohae launching station.

It announced the planned launch 11 days before and notified neighbouring countries including Japan of the intended flight path.

That launch triggered fresh sanctions and a surge in military tensions that culminated two months later in North Korea conducting its third nuclear test.

South Korean President Park Geun-Hye last month warned Pyongyang of serious consequences if it pushes forward with either a rocket launch or nuclear test.