Recent satellite images suggest that speculation North Korea will launch a satellite rocket on or before a key political anniversary next month is probably unfounded, US experts said Friday.

And while analysis of separate images showed new activity at the North's nuclear test site, the same experts said there was no indication it was linked to preparations for an actual test.

There has been fevered speculation for months that the North might launch a long-range rocket to mark the 70th anniversary of its ruling Workers' Party on October 10.

Hints dropped by the head of the North's space agency have fuelled the conjecture, while comments by the chief of the national atomic commission have led to additional talk of a possible fourth nuclear test.

The US, South Korea and its allies have made it clear that any rocket launch will be deemed a test of ballistic missile technology in violation of UN resolutions.

South Korean President Park Geun-Hye, who is expected to reference the North's missile and nuclear weapons programmes in an address to the UN General Assembly next week, warned Pyongyang of serious consequences if it pushed forward with either a rocket launch or nuclear test.

- 'Price to be paid' -

"Should the North go ahead with provocative actions that violate the UN Security Council resolutions, there will certainly be a price to be paid," Park told Bloomberg in a written interview before her departure for New York on Friday.

According to analysts at the US-Korea Institute at Johns Hopkins University, the latest satellite images of the North's Sohae Satellite Launching Station indicate that the prospect of a space launch vehicle (SLV) blasting off the pad on or before October 10 is possible but "unlikely".

"There are no signs at the launch pad or the Sohae facility of preparations to launch an SLV," they said in a post on the institute's closely followed 38 North website.

North Korea successfully launched a three-stage, Unha-3 satellite rocket from the Sohae site on December 12, 2012.

In that case, it officially announced its intention to launch on December 1, and notified neighbouring countries including Japan of the SLV's intended flight path.

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

North Korea has carried out three nuclear tests -- in 2006, 2009 and 2013 -- and a rocket launch sometime this year would be seen as opening the door to a fourth.

The US-Korea Institute analysts said satellite images showed fresh activity at the Punggye-ri nuclear site, but declined to draw any firm conclusions as to its purpose.

"It could be related to anything from maintenance work to preparations for another nuclear test," they said.

One event that is certain is a massive military parade being prepared in Pyongyang on the day of the October 10 anniversary.

The last such parade was held in July 2013 -- an intimidating, two-hour spectacle of military might and patriotic fervour, involving wave after wave of goose-stepping soldiers, tank batteries and missile launchers.

North Korea's state media announced Friday that Kim Jong-Un had approved a one-month salary bonus for all military personnel and "working people" to celebrate the party anniversary.