(Adds Japanese comment, background)
TOKYO, Feb 22 (Reuters) - The World Trade Organization on Thursday largely upheld a Japanese complaint against South Korea's import bans and additional testing requirements imposed on Japanese seafood because of the 2011 Fukushima nuclear disaster.
In a ruling that can be appealed by either side, a WTO dispute panel said that South Korea's measures were initially justified but that keeping them in place violated the WTO's sanitary and phyto-sanitary (SPS) agreement.
"Japan welcomes the panel's decision and hopes that South Korea will sincerely and swiftly take corrective action," Japan's Fisheries Agency and Ministry of Foreign Affairs said in a statement.
Japan, which has been in talks with other countries such as China and Taiwan that also have trade restrictions in place, plans to step up talks with them in light of the WTO ruling, a government official said.
Many countries have removed or relaxed restrictions on produce from Japan in the wake of the Fukushima disaster, which led to meltdowns at a nuclear plant and forced Japan to suspend some agricultural and fisheries exports.
Some countries have maintained bans on imports, but South Korea is the only one that Japan has taken to the WTO.
South Korea widened its initial ban on Japanese fishery imports in 2013 to cover all seafood from eight Japanese prefectures including Fukushima.
Japan launched its trade complaint at the WTO in 2015, arguing that radioactive levels were safe and that a number of other nations, including the United States and Australia, had lifted or eased Fukushima-related restrictions.
South Korea imported 10.9 billion yen ($102 million) worth of Japanese seafood in the year to August 2013 before it broadened its restrictions. Those imports then fell to 8.4 billion yen the following year, according to the Japanese government.
Either side can appeal the ruling within 60 days, otherwise South Korea will be expected to bring its treatment of Japanese seafood into line with the WTO rules.
Relations between Japan and South Korea, often testy, have soured in recent years. ($1 107.2300 yen) (Reporting by Yuka Obayashi; Additional reporting by Tom Miles in Geneva; Editing by Stephanie Nebehay and Hugh Lawson)