SEOUL, South Korea (AP) -- South Korea says it has so far failed to detect radioactive elements that may have leaked from North Korea's third nuclear test.
Seoul said Friday it will stop sea operations to collect samples but will continue monitoring at land stations. China and Japan have also been collecting air samples but have so far reported no success.
Analysis of airborne samples is crucial in determining whether Tuesday's detonation used uranium or plutonium. A uranium test would be seen as a major step forward for Pyongyang's nuclear program.
Collecting radioactive byproducts is a race against time because highly enriched uranium degrades quickly.
Test sites can be sealed to prevent leaks. No radioactivity was detected after Pyongyang's second test in 2009.
Japan's Defense Ministry says its fighter jets will continue collecting air samples.