POLICE have stepped up their intimidation of war reparation campaigners by detaining almost all activists in Beijing and Shanghai during Japanese Prime Minister Morihiro Hosokawa's three-day visit to China. Although Beijing yesterday released more than 100 elderly anti-Japan activists after two days of investigations, Shanghai police rounded up war reparation activist Bao Ge just before the Prime Minister's arrival in the east China city. The release of the elderly dissidents coincided with a report which said 500 intellectuals had signed a petition to the National People's Congress (NPC) calling for their release and a public apology by the police. According to Bao's friends, the 31-year-old medical researcher was picked up by police officers yesterday morning. Yang Zhou, a friend of Bao, said the activist had no plans to demonstrate or embarrass the Government during Mr Hosokawa's visit and he believed Bao would be set free soon after Mr Hosokawa left Shanghai. ''He [Bao] has no plans to do anything . . . But the authorities obviously don't want to see even the slightest trouble. Although the issue [war reparation] is not related to the Most Favoured Nation (MFN) debate, anything ugly could affect MFN,'' Mr Yang said. The 100 or so dissidents, whose average age is 65, were detained last Friday after they had petitioned Mr Hosokawa to issue a formal apology and to pay compensations. Bao last Thursday sent a similar petition to the Japanese Embassy in Beijing. The Chinese Government agreed to drop claims to Japanese compensation 22 years ago when the two nations restored diplomatic relations. But many Chinese citizens regard the deal as a sellout and are seeking billions of dollars in compensation from Tokyo. One source said police had released more than 100 representatives of the group, the China Civilian Preparatory Committee for Japanese Reparations, but sent them all under escort back to their home provinces. Another 100 locked in a south Beijing depot were also sent home. ''They were released on Sunday night but police are taking them home under supervision,'' the activist said, adding a Beijing-based war reparation movement activist, Tong Zeng, remained in police custody. Mr Yang said the strong reaction from the Government could backfire. He said that despite the leadership's disapproval, intellectuals such as Beijing scholar Xu Liangying were still able to challenge the authorities by putting out an open letter calling for the release of all political prisoners.