Fighting in the Yemen capital of Sanaa between forces loyal to President Ali Abdullah Saleh and troops who defected to the opposition entered its fifth day on Thursday and killed 15 people from both sides.

Four civilians died caught in the crossfire between Republican Guard troops under the command of Saleh's son Ahmed and defectors led by General Ali Mohsen al-Ahmar, witnesses and medical workers said, according to Al Jazeera.

Among the fatalities were two women and a man who fell to sniper bullets fired from rooftops near Change Square, where anti-government protesters are camped and continue to demand Saleh's resignation.

The fourth victim died from shrapnel wounds in a mortar shell explosion in the square. The mortar attack also wounded nine people and burned several tents of protesters.

In Sanaa's Al-Hasaba district, followers of tribal chief Sheikh Sadiq al-Ahmar and Saleh loyalist Saghir bin Aziz exchanged gunfire. Followers of bin Aziz positioned in the building of the interior ministry fired shells unto the houses of Sheikh Sadiq's brothers, who joined the fighting.

International mediators had tried to pacify both sides Wednesday with a proposed peace deal and political solution, but failed, and the fighting followed. United Nations envoy Jamal Benomar warned on an increasing risk of civil war, according to AFP.

The protest against Saleh started in January. He is currently in Saudi Arabia recuperating from wounds suffered in an attack the presidential palace on June. He refuses to resign and has vowed to return to his country.