South Korea and Japan made no progress in defusing mounting tensions over Tokyo's plan to send survey ships into waters claimed by both countries, but planned to keep talking, a South Korean diplomat said.

"We exchanged opinions, but failed to find common ground," South Korean Vice Foreign Minister Yu Myung-hwan said early Saturday after a series of talks with Japanese Undersecretary for Foreign Affairs Shotaro Yachi, who made an emergency trip to the South Korean capital Friday.

The two sides planned to break for the night and meet again later Saturday, Yu said.

Japan has reportedly agreed to delay the survey while the talks continue. Its coast guard survey ships had been scheduled to start the study as early as Thursday, but have waited off the coast as tensions flared.

South Korea has dispatched about 20 gunboats to the disputed waters, and has told Japan to stay away.

The disputed waters surround rocky outcroppings — called Dokdo by Koreans and Takeshima in Japan — that lie halfway between the countries and are claimed by both. The area, a rich fishing ground, is also believed to have methane hydrate deposits, a potential source of natural gas.

The showdown highlights the rising stakes of rival territorial claims in East Asia, and South Korea's deep-rooted bitterness over Japan's 1910-45 colonial rule.