TOKYO (Reuters) - An increasing number of fishing boats from North Korea has been appearing off Japan - some in distress, some abandoned and some with dead bodies on board - raising fears about infiltration by spies as tension with North Korea surges. The coastguard has beefed up patrols in response to the boats - including one labeled military property - just off the coast, or even grounded on Japanese beaches. The coastguard and analysts of North Korea have played down the fears, attributing the surge in boats to more mundane reasons, such as a North Korean drive to increase winter fish catches. But the worries persist.  The government is well aware that this is causing great anxiety to local people,  Chief Cabinet Secretary Yoshihide Suga told reporters this week.  The police and coastguard ... are working to clarify the situation,  he said.  Once we have the facts, we will respond firmly.  There were 28 cases of boats adrift off Japan s coast or grounded on its shores in November, the coastguard said, compared with four in November last year. One of the boats was a 14-metre wooden vessel from North Korea found off the northern island of Hokkaido with 10 crew on board. Raising alarm in a country North Korea has threatened to destroy, amid tension over its relentless development of nuclear bombs and missiles, was a square plate attached to the boat reading:  Korean People s Army, No. 854 military unit  in Korean script. Police and the coastguard questioning the crew declined to comment. A day before that boat was detained, eight decomposed bodies  were found in a small boat washed up on a beach. Also on board were life jackets bearing Korean lettering.    I have no intention to stoke fears,  opposition lawmaker Tetsuro Fukuyama told parliament on Tuesday, referring to another case when eight men who said they were from North Korea were found wandering along a marina..  What about the risk of these people, if they are special agents, making a landing just when some military operation is going on?  Analysts point to rising demand for fish in North Korea, and competition with Chinese boats, pushing North Korean fishermen further out to sea. North Korea is calling for bigger catches from fishermen sailing rough winter seas in small, old boats with unreliable engines. North Korea s Rodong Sinmun newspaper last month urged  fishermen to fight their  important battle  of meeting annual quotas in winter.  Fish are like bullets and artillery shells,  it said.  Nihon University professor Ken Kotani said he did not think the boats signaled a North Korean spy campaign, noting that local authorities were handling the situation.  The government has entrusted this to local police,  he said. Satoru Miyamato, professor at Seigakuin University, said he suspected growing demand for fish was luring more fishermen to sea in rickety boats.  The number of wealthy people is growing and they re seeking a healthy diet. Fishing is meeting that demand,  he said. 
North Korea boats off Japan spark spy scare; but some suspect just luckless fishermen