SEOUL (REUTERS, AP) -Japan on Wednesday (Sept 18) said South Korea's decision to remove Tokyo's fast-track trade status without sufficient explanation was "regrettable", as a diplomatic and trade row between the two Asian neighbours and U.S. allies deepened.

Earlier in the day, South Korea said it had approved plans to drop Japan from its "white list" of countries with fast-track trade status.

The decision, which wasn't accompanied by sufficient explanation, was "regrettable", Isshu Sugawara, the minister of economy, trade and industry, said in a statement.

South Korea has gone through with plans to drop Japan from a list of countries receiving fast-track approvals in trade in a tit-for-tat reaction to a similar move by Tokyo to downgrade Seoul's trade status amid a tense diplomatic dispute.

South Korea's trade ministry says Japan's removal from a 29-member "white list" of nations enjoying minimum trade restrictions went into effect on Wednesday (Sept 18).

The move comes a week after South Korea initiated a complaint to the World Trade Organisation over a separate Japanese move to tighten export controls on key chemicals South Korean companies use to manufacture semiconductors and displays.