The return of the Diaoyu Islands controversy, prompted by the recent collision between a mainland trawler with Japanese patrol boats in waters off the disputed islands in the East China Sea, is threatening to scuttle bilateral ties. And with the appointment of conservative hardliner Seiji Maehara as foreign minister in a Japanese cabinet reshuffle, many now fear Sino-Japanese ties will come under even more strain. This series of events coincided with the anniversary of Japan's invasion of Manchuria 79 years ago, on September 18. People in Hong Kong, the mainland and overseas Chinese communities took to the streets to denounce Japan's wartime atrocities. Despite rising anti-Japanese sentiment, Tokyo extended the detention of the captain of the Chinese fishing boat, saying it had to investigate the incident further. China has repeatedly raised the matter with the Japanese embassy in Beijing, to express its outrage. In retaliation, it has suspended bilateral exchanges at the provincial and ministerial levels, halted talks about increasing flights between the countries and postponed a meeting about coal. The row over the Diaoyus - the Senkakus to the Japanese - first flared up 40 years ago. Japan's claim to the islets was backed by the US-Japan Okinawa Reversion Treaty of 1971, which said the Diaoyus were part of Okinawa. Since then the sovereignty dispute has continued between mainland China, Taiwan and Japan, sometimes touching off ultranationalist, anti-Japanese sentiment. In the 1970s, Deng Xiaoping proposed setting aside territorial disputes and pursuing joint development - the approach that became the basis of the mainland's approach to boundary issues with Tokyo. This time around, Beijing, clearly concerned that flaring nationalism could backfire and damage bilateral ties, might have tried to adhere to a less confrontational stand. But its efforts to minimise the scale of protests across the mainland have failed to dampen nationalist sentiment both inside and outside the country. Hong Kong, under the principle of 'one country, two systems', doesn't have the power to administer its foreign affairs and defence issues. But that doesn't mean the city has to follow every step the central government takes in 'managing' Diaoyu-related protests. Our government has unashamedly tried to block the local Diaoyu movement and deter people from participating. Last year, activists from the Action Committee for Defending the Diaoyu Islands were barred from sailing to the disputed islets on the grounds that they were not fishermen. Many excuses have been used in the past, and the government's latest move was to allege there was a rat infestation on the activists' vessel - Diaoyu II. It has been rather sneaky in its attempts to stop the protest voyage. Recently it has deployed a marine police vessel to tail the fishing boat. It is outrageous for the administration to send Food and Environmental Hygiene Department officers to use administrative measures to crack down on political activities. And this was not the first time. The department tried to block a June 4 anniversary exhibition outside Times Square by saying protesters did not have a permit. Hong Kong is a free and open society that advocates respect for the rule of law and people's rights and duties. We should all stand firm to uphold these core values at all costs. The government's crafty and underhanded approach towards the Diaoyu issue will only fuel dissatisfaction or even public outrage. Albert Cheng King-hon is a political commentator. taipan@albertcheng.hk