Farc rebels in Colombia have killed at least 15 soldiers who were trying to destroy cocaine laboratories in the southern Caqueta region of the country.Another 11 soldiers were wounded in the clash. It is the worst defeat Farc has inflicted on the military this year.
The troops were attacked as they were dropped from helicopters.
The cocaine laboratories provide the rebels with their main income. The drugs are mostly moved south through Ecuador and sold to Mexican cartels.
Reports suggest the soldiers from the anti-narcotics brigade were confronted by a large, and heavily armed, guerrilla unit, which managed to disappear back into the jungle before the military was able to react.
Earlier this month, a senior rebel leader contradicted government suggestions the guerrilla group had been severely weakened, and said it remained ready for battle.
On Friday eight people including a baby were killed in two Farc attacks.
The BBC's Jeremy McDermott in Medellin says the rebels are trying to step up their actions and force the government to the negotiating table.
Since 2002 Farc has seen its numbers halved in the face of concerted attacks from the US-backed military. But in the last three years they have stepped up their attacks and re-taken the initiative in certain parts of the country, helped with income from the drugs trade and extortion.
Prelude to talks? The province of Caqueta is home to the Farc's Southern Bloc, one of seven fighting divisions spread across the country.
The area is also important for the cocaine trade, with guerrillas growing coca and processing cocaine.
In February Farc announced it was ending its policy of kidnappings, and earlier this month released 10 hostages who had been held for more than a decade.
The Farc commander-in-chief, Rodrigo Londono, better known by his alias of Timochenko, has offered to hold peace talks with the government. So far President Juan Manuel Santos has refused.
Our correspondent says the rebels may well be sending a message, warning him of what may happen if he refuses to negotiate.