"The Japanese government has recently notified us that it plans to conduct a survey for radioactive pollution in the East Sea (Sea of Japan) at an appropriate time," Ban told reporters.

"It is the clear position of our government that if Japan wants to conduct a maritime survey in our EEZ (Exclusive Economic Zone), it must seek our government's authorisation," he said.

The two countries have seen their ties strained over the past year over the island dispute. Some analysts have said the row has affected Seoul and Tokyo's efforts to bring North Korea back to talks aimed at ending Pyongyang's nuclear weapons programme.

Ban said he would visit Tokyo on Aug. 7 and hold talks with Japanese Foreign Minister Taro Aso on the nuclear issue.

Japan's top government spokesman said Japan had the right to conduct surveys near the islands.

"Our policy is to carry out a survey if necessary, at an appropriate time, but we have not made any specific decisions," Chief Cabinet Secretary Shinzo Abe told a news conference.

He added the survey for radioactivity has been carried out every year to find out about the maritime contamination.

South Korea's Yonhap new agency said that from the 1950s to the 1990s, the Soviet Union and then Russia dumped nuclear waste in waters off of Vladivostock. In 1994, Japan, Russia and South Korea conducted a survey in the Sea of Japan.

Japan has followed with yearly surveys

Last month, South Korea sent a survey vessel near the desolate islands claimed by both countries, which led to protests from Tokyo.

The islands called Tokto in South Korea and Takeshima in Japan lie about the same distance from the mainland of the two countries.

They are situated in rich fishing grounds and above deposits of gas hydrate -- a crystalline solid rich in methane -- which Seoul's state gas company said could be worth billions of dollars.

Following the dispatch of the South Korean survey vessel to the area, Japan said it may resurrect its own survey of the waters, which it called off in April following talks with Seoul.