Japanese police have raided the offices of a pro-North Korean organisation suspected of a role in the illegal shipment of computers to North Korea.
Japan maintains a total ban on exports to North Korea.
It is part of a range of sanctions over North Korea's nuclear programme and its abduction of Japanese nationals in the 1970s and 80s.
Earlier this month police arrested a businessman accused of exporting PCs to North Korea through China.
On Tuesday, about 100 riot police entered the Tokyo offices of an organisation connected to the Pyongyang-affiliated General Association of Korean Residents in Japan, officials say.
Because there are no diplomatic relations between the two countries, the association has functioned as North Korea's de facto embassy in Japan.[
The raid came after prosecutors last week indicted Lee Soon-Gi, 49, who is accused of illegally exporting 100 second-hand personal computers to North Korea through China, officials said.
The affiliate organisation may be involved in the shipments, police say.
But the association has strongly criticised the raid which it described as an "unjustified and illegal investigation".
Koreans form the second biggest ethnic minority in Japan after the Chinese. Many are the descendants of forced workers who came to Japan during the 1910 to 1945 occupation of the Korean peninsula.
North Korea has admitted it kidnapped Japanese nationals in the 1970s and 80s to train its spies.