Separatists in south Yemen killed the director of a criminal investigations unit in an ambush of 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 government of Yemen, the poorest country in the Arab world, is facing a secessionist movement in the south.
It has also been battling a Shi'ite insurgency in the north and a resurgent al Qaeda.
The northern rebels 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 the southern province of al-Dalea. No injuries were reported.
People in the south, home to most of Yemen's oil facilities, have long complained that northerners have abused a 1990 agreement uniting the country to grab their resources and discriminate against them.
Western governments and neighbouring Saudi Arabia, the world's biggest oil exporter, fear al Qaeda is exploiting the instability in Yemen to recruit and train militants to launch attacks in the region and beyond.
Reuters