South Korean Foreign Minister Ban Ki- moon on Tuesday postponed his visit to Mexico and El Salvador amid tension over territorial dispute with Japan.

"Ban decided to postpone the trip considering the need to handle various outstanding diplomatic issues," said Choo Kyu-ho, spokesman for the Ministry of Foreign Affairs and Trade.

The ministry will reschedule the visit, originally set for July 5-10, through consultations with the countries, the spokesman added.

Ban's decision was made one day after Japanese Chief Cabinet Secretary Shinzo Abe asked Seoul on Monday to make "sensible decision of exercising self-restraint," warning that Japan "will appropriately deal with the matter based on the UN Convention on the Law of the Sea and other relevant domestic laws."

A South Korean vessel launched a 12-day maritime survey in the East Sea (Sea of Japan) on Monday to collect data on salinity and sea temperatures in a square section of the waters between the two neighboring nations, including those near the disputed islets of Dokdo.

Japan also claims sovereignty over Dokdo, which Japan calls " Takeshima", and has repeatedly warned against South Korea's survey plan since it was announced on June 1.

Both South Korea and Japan claim waters near Dokdo to be its exclusive economic zone (EEZ).

South Korea has already tightened security around Dokdo since Monday and will take all measures to back the survey, the South Korean Coast Guard said Tuesday.

The ties between Seoul and Tokyo was heavily strained in April when Japan announced to carry out a maritime survey near Dokdo while South Korea strongly warned against it. Japan canceled the plan in late April after the two sides comprised on a pact through diplomatic contact.

In mid-June, South Korean and Japanese diplomats held a two-day negotiation over the exclusive rights to the waters around Dokdo in Tokyo but failed to make any breakthrough.

Dokdo, which has been controlled by South Korea since 1950s, lies 90 km southeast of South Korea's Ulleung Island and 160 km northwest to Japan's Oki island.

Source: Xinhua