North Korea has repaired extensive rain damage at its nuclear test facility and could conduct a detonation on two weeks notice, a US think-tank said Friday, citing satellite imagery analysis.

With the UN Security Council debating possible sanctions against the North following the launch earlier this month of a long-range rocket, there has been widespread speculation that Pyongyang may carry out its third nuclear test.

Satellite photos as recent as December 13 show that Pyongyang is determined to maintain a state of readiness at the Punggye-ri nuclear test site, the US-Korea Institute at Johns Hopkins University said.

Following heavy flooding earlier in the year that destroyed key infrastructure elements, the North has moved quickly to restore its ability to operate the complex, it said on its closely followed website 38 North.

"They continue to maintain the test site at a state of readiness that could allow them to conduct a detonation as soon as two weeks after such a decision is made," the institute reported.

However, it noted a possible "wildcard" in the form of a stream of water that appears to be coming from the entrance of the south tunnel at the test facility.

The flow indicates a possible problem with seepage that could adversely affect a nuclear device and sensors intended to gather data and monitor the test.

"Whether this problem is under control or has been solved remains unclear," it said.

The US and its allies have called for tough sanctions against Pyongyang for the rocket launch which they saw as a disguised ballistic missile test that violated UN sanctions imposed after the North's previous nuclear tests in 2006 and 2009.

Both of those tests were conducted in the wake of long-range missile launches.

The North's only major ally and main economic supporter, China, is resisting any significant tightening of sanctions already in place.

However, analysts say another nuclear test would severely test Beijing's patience with its unpredictable neighbour.