A mayor near Colombia's northern border with Panama said up to 200 bodies were found floating in the town's river after weekend combat between Marxist rebels and paramilitaries.
"Approximately, there are between 150 and 200 dead," said Mr Ricardo Azael Victoria, mayor of Riosucio, or "Dirty River".
His comments could not be confirmed by the local army, police or Red Cross officials. Paramilitary and rebel sources also could not confirm the reports.
In the past, Colombian mayors have often exaggerated the number of dead only to be corrected by Red Cross or government officials later.
Mr Victoria did not say whether the bodies were those of civilians, or camouflaged fighters who battle for control of Colombia's Choco province - a key pathway for arms and cocaine smuggling.
Colombia's 37-year-old guerrilla war has claimed 40,000 mainly civilian lives in the past decade, with the army, leftist rebels and paramilitary forces fighting for control of the Andean nation's countryside.