Police said the bomber arrived at the rally on a bicycle with the explosive hidden under his shirt. Upon detonation, ball-bearings were flung into the air in all directions. Such attacks have become the hallmark of Tamil Tiger rebels. Bloody campaign Mr Baithullah is the second candidate to be assassinated since parliament was dissolved in August ahead of elections next week. Last month, a candidate for the People's Alliance was gunned down by suspected Tamil Tigers in the eastern district of Batticaloa.
Officials say politicians have been warned of more attacks in coming days.
Trends so far suggest that this vote will be one of the bloodiest in recent times. There have been more than 800 cases of violence, with more than a dozen people killed in election-related attacks in areas which are otherwise regarded as relatively peaceful. The government and Tamil rebels are currently fighting for control of territory in the north of the country - although voting will not be taking place in these areas.