BEIJING (AP) — Chinese patrol boats have harried the Japanese Coast Guard many times a week for more than a month in an unusually relentless response to their latest maritime spat.

Four Chinese craft typically push to within hailing distance of Japan's ships. They flash illuminated signs in Japanese to press Beijing's argument that it has ancient claims to a set of tiny East China Sea islands now controlled by Tokyo. China says its craft have tried to chase the Japanese away at least once, although Japan denies any of its ships fled.

The huge uptick in incidents has brought the sides into dangerously close proximity, reflecting a campaign by Beijing to wear down Japanese resolve with low-level, non-military maneuvers but also boosting the risk of a clash.

Although China wields a formidable arsenal, it has yet to deploy military assets in such encounters. Instead, Beijing has dispatched ships from government maritime agencies — only one of which is armed — to keep a lid on gunfire. Those agencies are now receiving added attention, with new ships on order and a national call going out for recruits.

China says ships from its Marine Surveillance service are merely defending Chinese sovereignty and protesting illegal Japanese control over the uninhabited islands, known as Senkaku in Japan and Diaoyu in China. The missions began after Japan's government purchased three of the five islands from their private Japanese owner in September, enraging a Chinese government that saw it as an attempt to boost Japan's sovereignty claim. It also sparked violent anti-Japanese protests in dozens of Chinese cities.

China's short-term goal has been primarily to force Japan to at least acknowledge that the islands are in dispute — something it has refused to do — but the boost in patrols raises the likelihood of a bigger confrontation, said Wang Dong, director of the Center for Northeast Asian Strategic Studies at Peking University.

"I'm very concerned about the current situation. The possibility of escalation cannot be ruled out," Wang said.

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With emotions running high, any accident or miscalculation in these maritime missions could yield unexpected outcomes.

"One side might deploy a naval vessel in a support fashion, a move that the other would match," said M. Taylor Fravel of the Massachusetts Institute of Technology, who is closely following the dispute.

Japan has made it clear that it intends to meet the Chinese challenge in kind.

Japanese Coast Guard spokesman Yasuhiko Oku said the dispute was a factor behind the government's allocation last week of 17 billion yen ($212 million) to beef up the Coast Guard fleet with seven new patrol ships and three helicopters, though he said the new assets are not only for use around the islands.

Oku declined, for national security reasons, to say how many ships patrol the islands. But he said the dispute has been a "significant draw" on resources.

Tensions in the region were highlighted by U.S.-Japan naval exercises that began Monday at various locations, involving some 37,400 Japanese and 10,000 U.S. troops. At the same time, Japanese and Chinese diplomats were in consultation in the central Chinese city of Wuhan, the Japanese Foreign Ministry said.

China's Foreign Ministry said the exercises were "not conducive to mutual trust in regional security," and urged the parties to "do more that helps regional peace and stability."

Already, the near-constant presence of Chinese ships around the disputed islands has stretched the Japanese Coast Guard, which pulled out of a recent fleet review to free up ships for patrols. That's a victory of sorts for Beijing's vow to claim what it calls sacred territory, between Taiwan and Japan's Okinawa. Taiwan also claims the islands, which were under U.S. administration after World War II before reverting to Japanese control in 1972.

Chinese outrage stems partly from lingering resentment over Japan's brutal World War II occupation of much of China, feelings that are constantly stoked by China's education system and state-controlled media. But control of sea lanes and potentially rich undersea minerals are also at play, along with China's burning desire for respect as a world power.

China and Japan have no formal agreement on preventing unintended incidents at sea, making it easier for events to spin out of control as they did when a Chinese fishing boat rammed a Japanese cutter in 2010, leading to a diplomatic standoff and anti-Japanese protests in China.

U.S. Assistant Secretary of State Kurt Campbell said last week that the sides need to calm down. "It's incredibly important that both countries appreciate what they have built and step back from the brink," Campbell said in Washington.

Chinese craft entered waters near the islands for the third consecutive day on Sunday, marking at least the 11th incursion in recent weeks. The Japanese Coast Guard has described all the incidents as routine without a risk of clashes, and said none of its ships have backed down.

However, the Chinese government said last week that its boats had performed "expulsion measures" against Japanese ships.

"Chinese law enforcement vessels have a foothold in the waters around Diaoyu and are expanding their activities to safeguard Chinese sovereignty," China's stridently nationalistic Communist Party tabloid Global Times said last Wednesday. It called that a warning to the Philippines, Vietnam and other neighbors to "think twice before they provoke China."

Some scholars say China's apparent strategy to gradually erode Japanese control through low-key actions has been abetted by a non-committal response from Washington, who has said it takes no stance on the islands' sovereignty despite recognizing its treaty obligations to back Tokyo in a conflict.

China uses a similar approach in the South China Sea where it has maritime disputes with several other nations.

Earlier this year, Beijing managed to nudge the Philippines out of a disputed shoal by entering a lengthy but nonviolent maritime standoff. After both sides stood down, China set up barriers with ropes and buoys to block further access. Chinese ships have also sought to cut sonar cables and otherwise harass ships of the U.S. Navy.

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Associated Press writers Eric Talmadge and Mari Yamaguchi in Tokyo contributed to this report.