Army troops and federal agents detained 28 police officers for questioning in connection with the disappearance of two environmental activists in the southern state of Guerrero, Mexico's defense department said Friday.

Taken into custody were four Guerrero state police officers and 24 members of the municipal force in Tecpan de Galeana.

A federal judge ordered the arrests as part of the investigation into the disappearance of Eva Alarcon y Marcelo Bautista, the defense department said in a statement.

The activists were last seen Dec. 6 in Nuxco, a village outside Tecpan de Galeana.

Alarcon and Bautista are affiliated with an environmental group in Guerrero and with the nationwide Movement for Peace with Justice and Dignity, or MPJD, founded by poet Javier Sicilia to press for an end to the drug war that has claimed 50,000 lives in Mexico since December 2006.

The two missing activists were dragged off a bus while traveling to Chilpancingo, the state capital, according to the MPJD, which said it contacted Guerrero authorities on Dec. 7 to alert them about the pair's disapperance.

Bautista and Alarcon had sought police protection after receiving threats, the MPJD said.

Another MPJD member, Trinidad de la Cruz Crisostomo, was found dead on Dec. 8 in the western state of Michoacan.