SEOUL/TOKYO (Reuters) - Relations between U.S. allies South Korea and Japan deteriorated on Tuesday with South Korea questioning Japan’s commitment to U.N. sanctions against North Korea, while a South Korean legal case looked set to aggravate old wartime animosity.

FILE PHOTO - A police officer stands guard near Japan and South Korea national flags at hotel, in Tokyo June 22, 2015. REUTERS/Toru Hanai

Relations between the neighbors have long been plagued by memories of Japan’s 1910-45 colonization of the peninsula. In recent months, the question of compensation for South Koreans forced to work for Japanese occupiers has been a particular source of friction.

Ties between Washington’s two biggest Asian allies took a sharp turn for the worse this month when Japan restricted exports of high-tech materials to South Korea. The curbs threaten global supplies of memory chips and smartphones.

Japan has denied that the dispute over compensation for laborers is behind the export curbs, even though a Japanese government minister cited broken trust with South Korea over the labor dispute in announcing the export restrictions.

Instead, Japan has cited “inadequate management” of sensitive items exported to South Korea.

Japanese media reported that hydrogen fluoride, one of the three materials covered by the Japanese curbs that can also be used in chemical weapons, had been shipped to North Korea after being exported to South Korea.

South Korea denied that with President Moon Jae-in calling the reported accusation a “grave challenge”. The Japanese government has said it did not make any accusation about materials going to North Korea.

Nevertheless, South Korea hit back on Tuesday with the chief of its National Intelligence Service (NIS) telling a parliament committee on intelligence that Japan was very “lukewarm and passive” in terms of implementing U.N. sanctions.

The intelligence chief, Suh Hoon, told legislators Japan had recently allowed the entry of vessels suspected of making illegal ship-to-ship transfers of oil or coal products to North Korean ships in violations of U.N. sanctions, said Lee Eun-jae, one of the lawmakers briefed by the agency said.

A spokesman for the NIS confirmed that Suh had briefed the legislators but declined to give details.

A Japanese government spokesman was not immediately available for comment.

South Korea’s industry minister called on Japan to accept an independent investigation into the export control system, accusing Japan of failing to provide evidence to back up its accusation of “inadequate management” of export items.

The minister, Sung Yun-mo, also said in a Facebook posting he was ready to talk to Japanese Trade Minister Hiroshige Seko at any time and in any place.

OLD VICTIMS

Officials from the two sides met in Tokyo on Friday to discuss the export restrictions but they failed to make any progress. Instead, they have been exchanging rebukes about what each side said publicly after the five-hour talks.

Seko said on Tuesday it was regrettable that South Korea had given an erroneous account of the talks.

Japan lodged a protest with South Korea, saying it had broken an agreement on what the two sides would disclose, a Japanese trade ministry official said on the weekend..

Meanwhile, old acrimony over Japan's wartime behavior looks set to flare up again with South Koreans forced to work for Japanese occupiers seeking a court order to forcibly liquidate Japan's Mitsubishi Heavy Industries' 7011.T assets to compensate them, their lawyers said.

South Korea’s Supreme Court last year ordered the Japanese company to compensate 10 forced labor victims, drawing a strong rebuke from Japan, which believes the matter was settled under a 1965 treaty.

The lawyers said they would file court papers seeking the sale of Mitsubishi’s assets, as it had failed to respond by a Monday deadline to requests for discussions on the case.

“For plaintiffs who are over 90 years old, the process set by the law can no longer be delayed,” the lawyers said in a statement.

Mitsubishi Heavy Industries had no immediate comment.

The United States has for years sought a united stand with South Korea and Japan on standing up to what all three have long seen as North Korean aggression.

Over the past year, U.S. President Donald Trump has been engaging directly with North Korean leader Kim Jong Un in a bid to get him to give up his nuclear weapons.

David Stilwell, U.S. assistant secretary of state for East Asian and Pacific Affairs, told Japan’s NHK broadcaster on Friday the United States would not intervene in the dispute, but he encouraged them to settle it through dialogue.