Thirteen fighters were killed in an exchange of artillery fire between pro-government forces and separatists in the southern province of Abyan, military sources told AFP on Saturday.

The Southern Transitional Council lost eight men, including two officers, and six others were wounded late Friday in the latest outbreak of violence between the nominal allies in Yemen's civil war, an STC source said.

A military source on the Yemeni government side said that five fighters from its ranks were among the dead.

Tens of thousands of people, mostly civilians, have been killed and millions displaced in Yemen's conflict which has triggered what the United Nations has called the world's worst humanitarian disaster.