At least 28 Colombian soldiers were killed and another five remain missing after FARC rebels ambushed an army contingent in central-eastern Colombia, Defense Minister Camilo Ospina said.

The soldiers were attacked while monitoring efforts to eradicate illegal crops some 280 kilometers (174 miles) southeast of Bogota by rebels of Front 45 of the Revolutionary Armed Forces of Colombia (FARC), the spokesman said.

Military sources said at least five rebels were killed in the attack.

It was the most deadly attack by FARC rebels this year, and part of a campaign of attacks launched by the group since early December on roads in the country's northeast.

On December 17 FARC fighters killed eight policemen in an attack on a village and held 30 others captive for three days before they were freed.

According to some politicians, the rebels have stepped up their attacks to defend their countryside influence in advance of the coming legislative and presidential elections in 2006.

On November 27 President Alvaro Uribe, who has taken a hard line against the rebels, announced that he would stand for a second four-year term in the elections.

The 17,000-strong FARC army, together with the nearly 4,500-strong National Liberation Army (ELN), have sought to topple the Colombian government in more than 40 years of civil war that has left more than 200,000 people dead.

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Colombian Army soldiers. (AFP)