The director of a criminal investigations unit was killed in an ambush on his vehicle on Friday, security sources said.
Another person was killed and three injured in the shooting as they drove through a southern Yemen province, they said.
Further details were not immediately available.
The northern fighters and the government agreed last week to a truce to end a war that has raged on and off since 2004. Previous truces have not held.
In a separate incident on Friday, clashes erupted between security forces and unidentified gunmen in Aden. No injuries were reported.
People in the south, home to most of Yemen's oil facilities, have long complained that northerners have abused a union agreement to grab their resources and discriminate against them.
ReutersLast Mod: 20 Şubat 2010, 10:59