A South Korean ferry operator’s ban on Japanese passengers on its ferry service to Dokdo has irked Tokyo, aggravating tensions between two neighbors over the set of islands in East Sea.

South Korea has no right to ban Japanese nationals from boarding ships to Dokdo, a Japanese official said Friday.

The latest tension between the two neighboring states surfaced this week when a South Korean ferry operator said it will ban Japanese passengers from boarding its ships in protest against Tokyo’s recent territorial claims.

Japan has for decades laid territorial claims over Dokdo, which it calls Takeshima, worsening lingering resentment here since Tokyo’s 1910-45 brutal colonial rule.

The group of small volcanic islets lies in rich fishing grounds in the East Sea between South Korea and Japan, and are believed to contain large gas deposits.

The ferry operator Seaspovill Co. said that all Japanese citizens will be indefinitely barred from taking its ferries departing from Gangneung on South Korea’s east coast to Ulleung Island and the easternmost islets of Dokdo. Some reservations made by Japanese have already been turned down, it said.

Chiaki Takahashi, Japan’s State Secretary for Foreign Affairs, called the decision “inappropriate” during a press conference in Tokyo.

“As an ally nation, it is inappropriate for Korea to ban our people’s access to the ferry,” the official was quoted as saying by Japan’s The Yomiuri Shinbun. “If this is true, we will have to take necessary measures.”

South Korea’s top diplomat, meanwhile, said President Lee Myung-bak “could visit anywhere he wants in the country as head of the country,” indicating he might make such a decision.

“I don’t think there is any problem in him visiting our territory,” Foreign Minister Kim Sung-hwan said in a radio interview Friday. “I believe he will make decision based on his schedule and various other factors.”

A presidential aide had hinted earlier this week at the possibility of Lee visiting Dokdo, adding the president might mention the issue in his speech for the Aug. 15 National Liberation Day.

Minister Kim added Seoul was considering reinforcing the coast guard on the islets and setting up new facilities.

In a renewed attempt to claim ownership of the rocky islets, Japan described Dokdo as its territory in a new defense white paper on Tuesday, just a day after its politicians were sent back home under an entry ban by Seoul.

Lawmakers of Japan’s right-wing opposition party had attempted to visit the South Korean island of Ulleungdo ― located about 90 kilometers from Dokdo ― to see for themselves “how South Koreans feel” about the issue, only to be turned back by Seoul which said it could not guarantee their safety and did not want to escalate disputes.

The latest diplomatic tensions between the two countries started early last month when Japan imposed a one-month ban on the use of Korean Air flights by its diplomats in protest against the airline’s June 16 test flight of its first Airbus A380 above Dokdo.

Despite the South Korean Foreign Ministry’s effort not to let the issue damage ties with Tokyo to an extreme extent, a negative impact is feared especially in the ongoing regional cooperation over North Korea’s nuclear ambition.

Earlier this week, the U.S. government formally requested South Korea and Japan maintain “restraint” in resolving their latest diplomatic tensions over Dokdo.

“We would hope restraint would continue to be exercised and that they would ― both South Korea and Japan ― work peacefully and diplomatically to find a mutually acceptable solution,” State Department spokesman Mark Toner said at a press briefing Tuesday, emphasizing that Washington does not side with either.

By Shin Hae-in (hayney@heraldcorp.com)