Farmer Pedro Montes wears a machete on his hip to cut coca plants in Tierradentro, Colombia, in 2015. (Dania Maxwell for The Washington Post)

Colombian drug growers continue to stuff their fields with illegal coca ahead of a possible peace deal between the government and the leftist guerrillas who are dominant in the country’s narcotics trade.

The country’s coca crop increased 39 percent last year and has doubled since 2013, Colombian authorities said Thursday, announcing the results of an annual United Nations report that uses satellite data.

The government and its drug-war partner, the United States, hope that the coca boom is just a going-out-of-business blip as the Revolutionary Armed Forces of Colombia (FARC) and the growers in its territory try to make as much money as possible before renouncing the narcotics trade under the terms of a peace accord, which may be finalized in the coming weeks.

But the big harvest threatens to push a burst of cheap cocaine through the smuggling pipeline to the United States, the world’s largest drug consumer, while sowing new violence along the way. Colombia remains the single largest source of U.S. cocaine, producing more than Peru and Bolivia combined.

“The government won’t stand pat in the face of these statistics,” Colombian Defense Minister Luis Carlos Villegas told reporters Thursday evening.

“Growers have achieved higher productivity with their harvests,” he said, while blaming other trafficking groups for "orchestrating” protests against manual eradication by the impoverished farmers who insist they can't earn a living growing legal crops.

Colombia’s coca surge also raises fears that a bloody power struggle may emerge in the drug-growing areas long under FARC control as Colombian traffickers and other armed groups rush to take over the crops after the rebels demobilize.

Only in recent years have FARC commanders acknowledged their role in the narcotics trade, and according to Villegas, the biggest increases in coca production occurred mostly in the areas of southwestern Colombia dominated by the guerrillas.

Last year, more than 211,000 acres were covered in coca, the U.N. survey found, a seven-year high. Separate estimates by U.S. officials have put the figure even higher.

Colombian authorities say a perfect storm of factors is to blame for the bumper crop.

Growers appear to be planting as much coca as possible, anticipating that it will make them eligible for government financial assistance through crop-substitution programs that promote alternatives such as bananas and cacao.

They also privately suggest that FARC leaders may be trying to squirrel away as much cash as possible as they prepare to transition from life as insurgent fighters to civilian politicians. Lingering fears that the peace deal could fall apart creates another incentive to build up their reserves as a kind of guerrilla rainy-day fund.

It hasn’t hurt that Colombian authorities suspended aerial spraying of illegal crops last year, citing cancer concerns from use of the herbicide glyphosate. The flights were mostly piloted by U.S. contractors and were viewed as a pillar of the U.S. security strategy known as Plan Colombia.

But Colombian officials say spraying was becoming futile because growers have moved so much of the coca crop into national parks, indigenous reserves and other areas off-limits to spraying.

The government says it has stepped up manual eradication efforts instead. But farmers appear to be putting coca in the ground faster than authorities can rip it out.

Drought blamed on the El Niño phenomenon may have also prompted some farmers to plant more coca, which thrives in Colombia’s rough terrain and grows heartily despite adverse conditions.

The surge in coca production has prompted some rare public criticism from U.S. officials, who view Colombia as the top U.S. ally in South America. William Brownfield, the State Department’s top narcotics official, told the Senate Foreign Relations Committee last month that the government of Colombian President Juan Manuel Santos appeared to be wary of hurting delicate negotiations with the FARC.

Brownfield, a former ambassador to Colombia, called soaring coca output a setback and “a disturbing fact.”

“We have to acknowledge that as the peace process and the negotiations have developed for the last four years, one of the elements of the Colombian government policy that has not been maintained at its previous levels is counternarcotic and eradication efforts,” he testified.