SHANGHAI: Shanghai police have ruled out the possibility the May 5 blast on a bus that killed three people and injured 12 others was terrorist-related.

Vice-director of Shanghai public security bureau Chen Jiulong said on Wednesday, "unresolved conflicts" might have been behind the explosion.

The police had offered a 50,000-yuan ($7,500) reward for information about a man killed in the incident.

The bus burst into flames at about 9 am on May 5, as it was leaving a stop near the junction of Huangxing and Guoquan roads, Yangpu district.

Shanghai has heightened security in the lead-up to the Olympics, especially since the two bus explosions on Monday in Kunming, capital of Yunnan province, in which two people died and 14 others were injured.

By Aug 3, all 1,500 buses traveling past Shanghai Olympic venues will be equipped with a video monitoring system comprising four chromatic infrared cameras with a 15-day storage capacity.

As an Olympic co-host city, Shanghai will host nine men's and three women's soccer matches.

Plainclothes police will board buses and metro lines in the vicinity of Olympic stadiums during the Games and be ready to take action if they observe any suspicious behavior. Shanghai will also install more liquid and solid explosive detectors.

Police department official Yang Ye said Shanghai has set up an Olympics intelligence division, encouraging citizens to participate in the security campaign. Anyone reporting information to the police relating to violence, terrorism or other crimes will receive a reward of between 10,000 and 500,000 yuan.

The local Oriental Morning Post reported yesterday that Shanghai police had tracked down and disbanded "a group of terrorists".

Shanghai police, however, declined to give any details about this new development.