Colombian prosecutors Monday opened an investigation after President Juan Manuel Santos said more than 1,000 of his personal emails had been hacked, as spying allegations mar peace talks with the FARC rebels.

Santos claimed unknown parties were trying to slander him ahead of the May presidential vote, accusing them of breaking into his own email account as well as those of his family.

Prosecutors said Monday they will probe whether the suspected hackers are linked to a special Colombian army intelligence unit accused of spying on its own government's negotiating team at peace talks with FARC rebels in Cuba.

Those talks resumed in Havana Monday, with the rebels expressing their "great mistrust" of the intelligence unit's alleged spy efforts, saying it also monitors the FARC.

The disclosures of electronic eavesdropping touched off a political scandal in Colombia, with Santos declaring that the spying was "totally unacceptable" and warning that "dark forces" were intent on sabotaging the peace process. The government is investigating.

But the FARC, which has between 7,000 and 8,000 fighters, accused the Santos government of denouncing the spying in order to blunt the impact of its revelation.

The peace talks have been underway with the FARC for more than a year to end a half-century of hostilities.

Meanwhile, Colombia's second biggest group of leftist rebels, the National Liberation Army, or ELN, said Monday it captured a Colombian police officer during a government drug raid and promised to free him soon.

The 19-year-old police officer was captured in the Antioquia region, a major center of cocaine production, and was "in good health" and being treated in accordance with human rights protocols, the rebels said in a statement.

The ELN, which has about 2,500 fighters, did not say exactly when the police officer was taken.

And in central Colombia, a helicopter crash killed four soldiers on Sunday night, the army said in a statement Monday. The soldiers were conducting "military operations" in the region near Mesetas, it added, without giving any details.