Recent satellite imagery shows little activity suggesting North Korea is preparing for yet another nuclear test, but the communist nation could conduct one undetected at any time, a North Korea-monitoring site said Tuesday.

South Korea's main intelligence agency, National Intelligence Service, reported to lawmakers earlier this month that the North, which conducted its fourth nuclear test on Jan. 6, could carry out its fifth nuclear test explosion at any time.

The website 38 North said, however, that commercial satellite imagery taken between late January and early February 2016 of the North's Punggye-ri nuclear test site in the country's northeast reveals few if any signs of test preparations.

"Regardless, given the recent experience with the Jan. 6 test -- namely that North Korea appears to have altered its past test preparation practices in order to make them more difficult to detect -- it may well be that the North could conduct another detonation with little or no warning," 38 North said.

"In the month since North Korea's last test, there has been little observed activity at the Punggye-ri site," it said. "An examination of past imagery suggests that the North may have tunnels already completed and ready for a test should it decide to move forward."

Based on imagery observations alone, the Jan. 6 test showed the North can now conduct a nuclear test with little or no advance notice, the website said, adding that the North could have planned carefully to avoid detection by commercial satellites by instituting a practice of gradual, low-key preparations that took place over months.

"For example, imagery cannot reveal whether the tunnels are partially sealed with rubble or cement, 'stemmed,' during the maintenance or construction phases, or whether they are stemmed within the test preparation period," 38 North said.

"If they are already partially sealed, test preparation can proceed rapidly. They would simply need only to bring in the nuclear test device, prepare it, and do the final sealing, all largely unnoticed," it said. (Yonhap)