The soldiers were participating in anti-guerrilla exercises in central Colombia, including a task in which they had to cross the Magdalena River with rafts they built themselves, army officer Jorge Hernandez told Blu Radio.

One raft, with 11 soldiers on board, was swept away by a current and forced underneath a ferry docked on the shore.

Eight managed to escape, but three were sucked under the water.

Deaths during military exercises are not unheard of in Colombia, and analysts blame military equipment in poor condition.

In April, a soldier died in a helicopter crash in the country's north and in February eight lost their lives in a traffic accident in the southwest.

Colombia remains embroiled in a six-decade internal conflict pitting guerrillas, drug traffickers and the military against one another.