The North's Foreign Ministry says it has "no other choice but to develop and test the special armaments to completely destroy the lethal weapons reinforced in South Korea".
United States officials said they would "do everything we can" to ease tensions, without offering a specific opinion on Japan's measures.
"If the investigation shows that our government did something wrong, we will immediately apologise and rectify the situation", Mr Kim said.
The official said he and his colleague asked to start negotiations for the removal of the measures, but the Japanese refused.
It plans to file a complaint with the World Trade Organization and has denied the Japanese allegations that it allowed sensitive materials to reach North Korea.
"In the meeting with President Trump in Osaka, President Xi briefed him on China's principled position on the peninsula issue, and pushed the USA side to show flexibility and meet the North Koreans half way, including easing sanctions in due course", Geng said.
The meeting started in an icy atmosphere, with officials skipping handshakes and staring at each other across the table in silence for several minutes, and continued for almost six hours.More news: Pence deplores 'crisis' at US migrant camp
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The South Korean government proposed on Friday, . that Seoul and Tokyo should be jointly investigated by an worldwide body on their sanctions enforcement.
However, a Japanese Ministry of Foreign Affairs official yesterday said that the curbs on exports of the materials were not retaliation in the feud over compensation for South Koreans forced to work for Japanese firms.
But at a hastily-called press conference after the comment by the South Korean official, an official at the Japanese Ministry of Economy, Trade and Industry said such a request was not made in explicit terms. When pressed by South Korean officials, the Japanese officials said the cases were unrelated to illegal shipments to a third country but refused to provide details, Lee said.
He noted that if the global probe finds no violation, the Japanese government should immediately apologize to and retract its export restrictions on South Korea, which he called "retaliatory in nature". "We did not see any willingness by Japan to change its measures from this meeting".
Last year, South Korean courts ordered Japanese companies, including Mitsubishi, to pay for using slave labor during the Japanese occupation of Korea.
This is according to the Voice of America on Saturday, . citing a State Department official.
The South Korean Ministry of Trade, Industry and Energy on Wednesday said that it had found 156 cases of unauthorized exports of strategic goods as of March 2015, but none involved North Korea.