TOKYO • The feud between Japan and South Korea continued to escalate yesterday.

Seoul went on a diplomatic charm offensive at regional conferences in Bangkok and Beijing over Tokyo's decision to expel South Korea from its trade whitelist over security concerns.

Japan reacted with disapproval, calling on South Korea not to raise unrelated matters at multilateral meetings.

South Korean Prime Minister Lee Nak-yon said in Seoul yesterday that Japan "crossed a line it should not have", adding that his country will seek support from other nations over what he described as "unfair treatment" by Japan.

In Beijing, where a ministerial meeting was held for the 16-nation Regional Comprehensive Economic Partnership (RCEP), South Korean Trade Minister Yoo Myung-hee reportedly broached Japan's export controls twice.

Her Japanese counterpart Hiroshige Seko later said it was "extremely regrettable" that she had raised assertions with "no connection with the RCEP negotiations".

Likewise, in Bangkok, South Korean Foreign Minister Kang Kyung-wha raised the issue at a meeting with counterparts from five countries in the Mekong region.

Japanese Foreign Minister Taro Kono, who had a separate meeting with the Mekong nations, told reporters that the US and Asean "can easily understand Japan's action from the security point of view", as there have been no complaints.

Reuters quoted a senior South Korean official as saying in Bangkok yesterday that all options are on the table, including scrapping an intelligence-sharing pact. But the official also urged a "cooling-off period". "It's difficult to think about a long-term strategy under such a heightened, agitated situation."

Kyodo news agency, meanwhile, cited a US official as saying last Friday that Washington "has no interest in arbitrating or mediating" in the dispute.