The port town of Tumaco on Colombia's Pacific coast went dark for more than a week in early August after guerrillas toppled three electricity towers in the remote area.

Rebel-planted land mines did even more damage, delaying the restoration of power while killing at least five people, including two workers trying to repair the towers, local authorities said.

Such attacks on electricity infrastructure, gas pipelines and trains transporting coal occurred almost daily in the 1990s, and into the 2000s, as Colombia's rebel groups targeted the energy industry either to extort funds or attack foreign companies considered to be exploiting the nation's riches.

The attacks by the Revolutionary Armed Forces of Colombia, or FARC, the largest rebel force in the country, and the smaller National Liberation Front, or ELN, eventually fell off. But such rebel sabotage has been on the upswing again — a sign to some that the guerrillas have grown desperate as their armed strength has waned. The attacks have also hit as Colombia tries to build its economic future around increased oil production.

"The terrorists are still keeping it up to remain visible, undertaking certain limited, isolated actions that attempt to demonstrate a force that the country understands they do not have," Defense Minister Jose Carlos Pinzon said Wednesday of the most recent attacks.

Meanwhile, FARC representatives prepare for peace talks with Colombian authorities next month in Oslo, Norway, and have proposed a cease fire that could end the attacks on energy targets. President Juan Manuel Santos, however, has ruled out such a cease-fire, saying he has asked the military to instead step up their actions.

"We're not going to give up until we have a final accord, and that's clear," Santos said.

The energy and mining sector represents about 70 percent of the country's exports, with petroleum sales alone totaling at least $32 billion annually. The sector generates 12 percent of the country's gross domestic product, money that's key for development projects ranging from the construction of highways and bridges to low-income housing.

No estimates exist on how much damage the sabotage causes annually, but if a peace agreement is signed, Colombia's gross domestic product could grow an additional one or two percentage points, helping the country reach annual economic growth of 5 to 6 percent, according to Treasury Minister Mauricio Cardenas, a former minister of energy and mining.

Cardenas downplayed the impact of the attacks but still acknowledged they have had a cost, preventing the production of at least 15,000 barrels of crude daily. He denied they were a key reason for Colombia's failure to reach its production goal of a million barrels daily, saying bureaucratic delays in issuing environmental permits for oil projects were more to blame.

Neither the ELN nor the FARC has commented on the recent increase of attacks.

So far, the guerrillas have focused on infrastructure such as cargo trains and pipelines, leaving untouched facilities used to extract coal or pump oil from the ground. That's still hurt overall petroleum production, slowed exports and delayed plans to bring electricity to entire communities.

The attacks on pipelines have mushroomed by 253 percent, from 19 in the first half of 2011 to 67 in the same period this year, according to Defense Ministry data. There were 84 pipeline attacks last year, two less than the 86 recorded in 2002 when the FARC's armed strength was unquestioned.

The number of energy towers targeted by rebels rose from 39 in 2010 to 73 last year.

Carbones del Cerrejon Limited's rail line from its primary coal mine has suffered at least six attacks since January of this year, up from two in 2011, said Julian Gonzalez, the company's vice president of public affairs. The 150-kilometer (93-mile) track stretches to Puerto Bolivar on the Caribbean, where coal is loaded onto ships bound for the United States and Europe.

Alfredo Rangel of Colombia's Security and Democracy Foundation, which studies internal conflicts, said the increase in attacks began about two years ago, spiking this year as the military reduced its offensive actions. Rangel said that according to his own calculations and press reports, there were as many as 1,800 such military operations in 2003, plunging to about 360 last year.

Both Santos and Pinzon insist that the government has not let down its guard. According to Pinzon, 70 percent of the rebel activity occurs in just 50 of about 1,000 municipalities in the country.

Still, energy companies are beefing up security to protect their facilities.

The country's largest crude oil field, Puerto Gaitan, is guarded by at least 800 soldiers located inside the vast complex where 14,000 people work, said Federico Restrepo, vice president of corporate relations for the Toronto-based company Pacific Rubiales Energy. The firm holds a 35 percent stake in Puerto Gaitan, which produces about 20 percent of the country's daily production, set at an average of 918,000 barrels in August. Restrepo said none of the company's Colombia operations have suffered attacks.

Similar security has accompanied construction of a new pipeline called Bicentenario, which is being guarded meter by meter, even from above with military drones, Cardenas said. The proposed pipeline is set to be the country's longest, at 960 kilometers (597 miles), capable of carrying 450,000 barrels daily from the oil fields in Colombia's west to the Caribbean port of Convenas, according to Ecopetrol, a majority partner in the project.

Despite the patrols, the ELN in July briefly kidnapped two women working on the pipeline, releasing them 20 days later to the International Red Cross Committee.

Nationwide, at least 5,000 uniformed security forces guard Colombia's oil pipeline network, energy towers and even convoys of trucks transporting petroleum to refineries, said Cardenas.

Pinzon announced Wednesday that the Defense Ministry is creating eight new battalions to shore up security of the nation's infrastructure. A high-ranking official speaking on condition of anonymity because he was not authorized to comment publicly about national security issues said each battalion will be comprised of at least 1,200 troops, and three battalions are already operating.

Despite the attacks and the mounting security burden, the companies say they have no intention of leaving the country.

"After $8 billion of investment," said Restrepo, "we're staying."


Associated Press writer Cesar Garcia in Bogota contributed to this report.