North Korea announced Wednesday that it carried a “successful” test of a miniaturized hydrogen nuclear device, marking the country’s fourth nuclear test and an apparent improvement in its nuclear program.
The announcement was made at noon local time (10:30 p.m. ET Tuesday), just hours after seismologists detected a seismic event near the Punggye-ri nuclear test site in North Hamgyong province.

Specific details about the nuclear test were not immediately available, but it follows plutonium-fueled nuclear tests in October 2006, May 2009 and February 2013. Wednesday’s test is certain to provide international condemnation and prompt a new round of UN sanctions.