BOGOTA, Aug. 8 (Xinhuanet) -- A bomb exploded in Medellin, the second largest city of Columbia, on Sunday, injuring at least 21 people, including seven children.

    A spokesman for the Medellin government said thousands of citizens crowded the city center to watch the singing, dancing andparade marking the 47th Flowers Festival of Columbia.

    When the paraders were crossing a bridge, a bomb placed on it beforehand suddenly exploded, injuring 21 people, 10 of them seriously.

    Police and Red Cross aid workers rushed to the scene and took the wounded to nearby hospitals. Police also sealed off the scene and sent forces there to control the traffic.

    So far, no group or individual has claimed responsibility for the explosion. But police assumed that it was done by the Revolutionary Armed Forces of Colombia (FARC), the largest rebel group in the country.

    Colombia has been plagued by a four-decade-old civil war, in which leftist rebels, far-right paramilitaries and government troops fight one another. According to official statistics, about 3,500 people are killed every year and most of them are civilians.

    At present, the two guerrilla groups FARC and the National Liberation Army of Colombia are still fighting government forces. Enditem