The Colombian government says that the father of Liverpool footballer Luis Díaz was kidnapped by left-wing rebels of the National Liberation Army (ELN).
Luis Manuel Díaz was seized at gunpoint along with his wife on Saturday.
The player's mother was left behind in a car by the kidnappers as police closed in, but the gunmen dragged away his father.
Hundreds of police and soldiers have been deployed to free him.
Police had originally said that a criminal gang was most likely to blame.
But on Thursday, a government delegation which is currently engaged in peace talks with the rebel group, said that it had "official knowledge" that the kidnapping had been carried out by "a unit belonging to the ELN".
A representative of the group has reportedly said the group will free Díaz's father in the coming days.
The ELN is Colombia's main remaining active guerrilla group. It has been fighting the state since 1964 and has an estimated 2,500 members.
It is most active in the border region with Venezuela where Luis Manuel Díaz and his wife Cilenis Marulanda live.
CCTV footage showed their car being followed by men on motorbikes on Saturday afternoon.
The couple was accosted by the gunmen as they had stopped at a petrol station in their hometown of Barrancas, in the northern province of La Guajira.
The kidnappers later abandoned Luis Díaz's mother in a car as police closed in, but dragged away his father.
Police have focussed their search on the Serranía del Perijá, a mountainous area straddling the Colombia-Venezuela border.
They have found two motorbikes and a car they think were used in the kidnapping but have yet to pinpoint Luis Manuel Díaz's whereabouts.
In his statement [in Spanish], the head of the government delegation negotiating with the ELN, Otty Patiño, demanded the "immediate release of Luis Manuel Díaz.
"We remind the ELN that kidnappings are criminal acts which violate international humanitarian law and that it is their [the ELN's] duty as part of the current peace process to not only stop engaging in kidnappings but also to forever stamp them out," the statement reads.
Previous attempts at reaching a peace deal with the ELN have failed but as part of President Gustavo Petro's strategy for "total peace", his government restarted talks with the guerrilla group.
Earlier this year, the two sides agreed on a bilateral six-month ceasefire which came into force on 3 August.
The kidnapping of Luis Díaz's father has caused outrage in Colombia, where the player - who is part of Colombia's national team - is immensely popular.
His Liverpool team has also shown its unwavering support, with manager Jürgen Klopp dedicating Sunday's 3-0 Premier League victory over Nottingham Forest to Díaz, saying they had won "for our brother".