Colombia's leftist ELN guerrilla group claimed to have kidnapped four geologists missing since last week in the northeast of the country.
The abductions come as the National Liberation Army (ELN) is conducting talks with authorities aimed at starting a peace process.
The victims work for a subcontractor of the Colombian Geological Service and were snatched last week in a remote area in the Norte de Santander area, where the ELN has a strong presence.
They were taken "as they were getting ready to carry out studies on mining," the ELN said in a statement to a local radio station. The guerrillas added that they had acted to protect natural resources.
The geological service confirmed to AFP that the workers, three Colombian men and a woman, were missing.
Together with the FARC, the ELN is one of two leftist guerrilla groups in Colombia. Its fighters are mostly located in rural areas.
Colombia's internal conflict, the longest-running leftist insurgency in Latin America, has killed some 220,000 people and displaced 5.3 million.
The FARC has been in peace talks with the Colombian government since November 2012.