Bogotá, May 17 (RHC), – Colombia's Revolutionary Armed Forces (FARC) guerrillas reached a landmark agreement with the government toward eliminating the illegal drug trade and called a weeklong ceasefire on Friday, giving a political boost to President Juan Manuel Santos in his re-election bid.

The unilateral ceasefire includes the first round of presidential elections on May 25, where the center-right Santos' lead has virtually evaporated with the rise of right-wing rival, Oscar Ivan Zuluaga, now tipped to win in two recent surveys if, as expected, the voting goes to a second-round runoff on June 15.

While Santos has staked his political future on the talks, Zuluaga has threatened to end them if he wins.

Friday's agreement on the issue of illegal drugs puts the two sides one step closer to ending Latin America's longest-running guerrilla war. Rebel and government negotiators meeting in Havana are seeking to end a conflict that has killed more than 200,000 people since 1964.

They agreed to cooperate on eradicating illicit drug cultivation through crop substitution, a departure from the forced destruction of coca fields, often by spraying herbicide. The FARC opposes the chemical destruction of coca, and the government promised to spray fields only as a last resort.

They also reached a deal on the prevention of drug use and a solution to the production and sale of narcotics.

Chief government negotiator, Humberto de la Calle, called the deal a "landmark" and celebrated what he called a "dream," the possibility that the entire country would "work toward the same goal, in this case, a country without illegal crops and without drug trafficking."

Colombian President, Juan Manuel Santos, also celebrated the advance: "This is the furthest we have ever come on the path to ending our war," Santos said in a televised speech. "Can you imagine a Colombia without coca? This is within reach of our hands if we implement these agreements."

Negotiators have now reached accord on three of the five phases of the talks. Agricultural reform and the rebels' participation in politics were agreed last year, while reparations for war victims and the mechanics of ending the conflict remain the outstanding issues.

Santos rival, Zuluaga, an ally of influential former President Alvaro Uribe, has condemned the negotiations and promised to suspend them until the rebels call a definitive ceasefire and accept jail time.