Speculation over a new test, following a failed launch in April, has intensified in recent weeks and drew a sharp warning Thursday from the UN Security Council to Pyongyang.

The US-Korea Institute at Johns Hopkins University said new images provided by satellite operator DigitalGlobe clearly pointed to advanced launch preparations at the Sohae satellite launch station.

"If Pyongyang follows past practice in preparing for a launch, it could be ready to fire a rocket as early as the end of the first week in December," Nick Hansen, an expert on imagery analysis, wrote on the institute's website 38 North.

"(This is) a clear indicator that the rocket stages are being checked out before moving to the pad for an eventual launch," Hansen said.

Empty tanks spotted at four locations indicated that the propellant buildings at the pad have likely been filled in preparation for fuelling the rocket, he added.

In Seoul, a senior government official said South Korea believed preparations for a test had "entered a final stage".

"But there is no telling whether or when it would go ahead," the official, who declined to be identified, told AFP.

North Korea is known to have an inter-continental ballistic missile (ICBM) in development -- the Taepodong-2 -- but it has never been tested successfully.

On Thursday, the UN Security Council warned North Korea against carrying out another launch bid.

"We all agree it would be extremely inadvisable to proceed with the test," the head of the North Korea sanctions committee at the council, Portuguese Ambassador Jose Filipe Moraes Cabral, told reporters.

The latest satellite images were taken on November 23 and 26, and several experts suggested Pyongyang had accelerated test preparations ahead of a rocket launch by South Korea scheduled for November 29.

The South's launch was postponed at the last minute due to a technical problem and a new mission date has yet to be finalised.

US analysts like Scott Snyder, a senior fellow of Korea studies at the Council for Foreign Relations (CFR), say Pyongyang is particularly sensitive to what it sees as a double standard on missile and rocket testing.

"The fact that South Korea is able to pursue such launches while North Korea is prohibited from doing the same under UN Security Council Resolutions, is perceived in North Korea as exhibit number one of a discriminatory US policy," Snyder wrote on the CFR website.