TOKYO (AFP) - A lawmaker from Japan's ruling party was aboard one of four fishing boats that sailed on Monday towards islands at the centre of a bitter dispute with China, the organiser said, as Chinese vessels loomed nearby.
Japan's national broadcaster said one of the Chinese maritime surveillance ships had been within a kilometre of the fishing boats, in an incident that could inflame a debilitating international row.
There was no attempt by anyone on board to land on any of the islands, which Japan controls as the Senkakus, but which China claims as the Diaoyus.
"The purpose of dispatching the fishing boats is to fish in the waters," an official from the nationalist Channel Sakura satellite broadcaster told AFP, adding the company's president was aboard one of the boats.
"Most of the people on this mission are fishermen," he said, but noted that Kenji Yamada, a parliamentarian and member of Prime Minister Shinzo Abe's Liberal Democratic Party had also taken part in the mission.
The Japanese boats had left the area by the afternoon, he said.
The incident passed off without confrontation but marked a change from recent months, which have seen regular forays by official Chinese ships into the 12-nautical-mile zone regarded as territorial waters.
It has become customary for Japan's coastguard and the Chinese ships to exchange demands that the other side leave the waters, as part of a tussle between Tokyo and Beijing over ownership of the resource-rich islands.
A Japanese foreign ministry official telephoned the Chinese embassy in Tokyo to protest at the presence of the Chinese vessels, the ministry said.
The four ships made a circuit of the largest island in the chain before heading away, Japan's coastguard said.
A territorial row that dates back four decades reignited last September when Tokyo nationalised three islands in the chain, in what it said was a mere administrative change of ownership.
But the incident provoked fury in Beijing, which maintains the Senkakus were illegally snatched by Japan as it built an empire in the half-century before World War II.
Tokyo says it annexed an unclaimed archipelago that showed no signs of ownership.
Commentators say the islands are a potential flashpoint for a military confrontation between Asia's two largest powers.
They say the occasional presence of nationalists from both sides introduces a wild card that increases the risk of a misstep by one of the armed official vessels, which could quickly escalate.
Separately, the Japanese coastguard said a Bahamas-registered marine research vessel, Discoverer2, was in the exclusive economic zone (EEZ) of the islands.
The zone is a 200-nautical-mile area around a territory over which the sovereign nation has exclusive rights to exploit resources.
The ship, which is believed to belong to a Chinese oil company, has been spotted in the zone of the islands twice already this year and has been seen lowering wires into the water, a coastguard official said.
"In response to our warnings, the vessel's crew say it is operating with the approval of the Chinese government as the area is part of China's EEZ," he said.