North Korea is criticizing organizers of the World Economic Forum in Davos for revoking an invitation to its delegation in the wake of a nuclear test.

The WEF sent an invitation to North Korea last autumn but withdrew it after Pyongyang defiantly conducted its fourth nuclear test last week.

The North says its permanent representative to the U.N. office sent a letter of protest to the WEF's managing board on Thursday.

The official Korean Central News Agency says the letter expressed "deep concern" over the forum's decision and described it as a "very sinister act."

The annual WEF meeting scheduled for later this month is expected to draw more than 2,500 participants from more than 100 countries.