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

SEOUL (Reuters) - South Korea denied on Monday that one of its warships had locked its targeting radar on a Japanese patrol plane, which drew a strong protest from Tokyo amid increasingly frosty relations between the regional neighbors.

Last week’s alleged radar incident joined a list of issues discussed by diplomats from the two countries at a meeting in South Korea’s capital Seoul on Monday.

Relations between the two U.S. allies have soured since South Korea’s top court ruled in October that a Japanese steel firm must compensate four South Koreans for their forced labor during World War Two. Japan denounced the ruling.

On Friday, Japan’s defense minister said a South Korean destroyer had locked its targeting radar on a Japanese patrol plane, calling the action extremely dangerous.”

South Korea’s defense ministry, which said last week the destroyer was performing routine operations, on Monday provided more details of the vessel’s actions.

While rescuing a distressed North Korean fishing boat, the destroyer had used an optical camera that detected a low-flying Japanese patrol plane, an official from South Korea’s Joint Chiefs of Staff told reporters.

“During the process, there was no emission of radio waves at all,” the official said, denying that the warship had locked its tracking radar on the Japanese aircraft.

South Korean diplomats explained the situation “in detail” to their Japanese counterparts on Monday, and “the two sides agreed to continue to communicate as needed about this issue,” news agency News1 reported, citing an unnamed South Korean foreign ministry official.

The diplomats also discussed the North Korean nuclear issue and how Seoul and Tokyo could help restart talks between the United States and North Korea, South Korea’s foreign ministry said in a statement.