Supporters of the southern Yemeni separatists demonstrate against the government in Aden, Yemen January 28, 2018. (Photo: Reuters)

At least nine people were killed on Monday in heavy fighting between separatist forces and government troops in Yemen's interim capital of Aden, military sources said.

Five pro-separatist fighters were killed by snipers, while four soldiers died in clashes, the sources said, as both sides began using tanks and heavy artillery in a second day of fighting in the southern port city.