BOGOTA (Reuters) -- At least 40 soldiers and 10 peasants were reported
                  to have died when Marxist rebels launched a new bid to storm the mountain
                  stronghold of Colombia's top right-wing death squad chieftain, authorities
                  said late Tuesday.

                  About 500 Revolutionary Armed Forces of Colombia (FARC) guerrillas
                  attacked four hamlets in northern Cordoba province Monday, killing 10
                  peasants and razing a number of homes, according to Mario Carrascal,
                  mayor of Puerto Libertad, a town close to the combat zone.

                  The heaviest clashes occurred late Tuesday when army troops poured into
                  the area to hunt down the rebel unit. A spokesman for the army's 11th
                  Brigade said at least 40 soldiers were feared to have died in a FARC
                  ambush.

                  Military sources said the FARC had been attempting to push into the Nudo
                  de Paramillo mountain range, the power base of its most bitter enemy,
                  Carlos Castano, head of an illegal alliance of ultra-right wing death squads
                  known as the United Self-Defense Forces of Colombia (AUC).

                  Castano has spearheaded a "dirty war" against Colombia's estimated 20,000
                  guerrillas and their suspected sympathizers.

                  If the death toll is confirmed it would be one of the heaviest defeats for the
                  army this year.

                  The FARC overran Castano's mountaintop fortress last December, killing
                  and mutilating 30 peasants, but narrowly failing to capture Castano. It was
                  not immediately known if Castano was involved in the latest clashes.

                  The FARC is currently taking part in peace talks with the government in an
                  effort to find a negotiated settlement to the country's three-decade-old civil
                  conflict, which has claimed more than 35,000 lives in just 10 years.

                  But the rebels have said the negotiations must go ahead "in the midst of war"
                  and have repeatedly said they will not declare a cease-fire.

                  In a separate incident of political violence, 13 peasants were slain by
                  unidentified gunmen in a rural area near the town of San Carlos in northwest
                  Antioquia province Monday.