The four were being detained near the oil town of Brega, according to information received from HRW personnel in the zone, said spokesman Peter Bouckaert.
The journalists were travelling in a car when an artillery blast forced them to stop. At that point, the Gaddafi loyalists detained them and took them away in two vehicles, he said.
The HRW had gotten in contact with representatives of the Gaddafi government in an attempt to get the journalists released.
Spanish Foreign Minister Trinidad Jimenez said that when the government learned of the Spanish journalist's disappearance it began working to determine his whereabouts.
The government has been in contact with the European Union so that it could work to help get the matter resolved.
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