Colombia's ELN rebel force said on Friday it had made an "error" earlier in the day when it announced the release of two Dutch journalists kidnapped in the country's north four days ago.

The pair remain "in perfect condition," the rebel group's radio station ELN Ranpal said on Twitter about the case, that was the latest in a series of incidents which officials feared could disrupt peace talks the National Liberation Army (ELN) is holding with the Colombian government.

"On the captured Dutch men, we had received a report at noon on their release but we have not been able to corroborate it properly," the station said.

"We apologize and reiterate that the two foreigners are in perfect condition and in a short time there will be a positive outcome."

"The error was that Ranpal had received a report and did not corroborate it through internal channels."

The ELN had announced at midday Friday that Derk Johannes Bolt, 62, and his cameraman Eugenio Ernest Marie Follender, 58, had been freed. But local journalists began to question the account when authorities did not confirm their release after more than six hours.

The men were kidnapped Monday near the Venezuelan border.

The governor of the surrounding Norte de Santander district, William Villamizar, said Thursday a humanitarian commission was mediating their release.

The government's chief negotiator with the guerrillas, Juan Camilo Restrepo, warned Tuesday the kidnapping complicated negotiations with the ELN that began in February.

Villamizar said the military and the ELN had been asked to reduce their operations in the area "so as not to endanger the lives of the Dutch journalists" in order for them to be released safely.

The journalists work for Spoorloos, a program on Kro-Ncrv TV that helps Dutch people trace their biological relatives around the world.

In May 2016, ELN rebels kidnapped a Colombian-Spanish journalist and two Colombian TV reporters in the same region. They were handed over to intermediaries a few days later.

In the main thrust of Colombia's peace drive, the country's biggest rebel group, the FARC, is scheduled to complete its disarmament by June 27 under a peace deal it signed last year.

Colombia's President Juan Manuel Santos said the FARC would complete their historic disarmament on Friday. He spoke during an official visit to France.

But UN observers had yet to confirm the formal end to the disarmament process.

The Colombian conflict erupted in 1964 when the FARC and the smaller ELN took up arms for rural land rights.

The violence drew in various rebel and paramilitary forces and drug gangs as well as state forces.

The conflict has left at least 260,000 people dead and displaced more than seven million, according to authorities.