Yemeni security forces and loyalists of an opposition tribal chief have clashed on the outskirts of the capital, Sana'a.

Witnesses say hundreds of tribesmen loyal to Sheikh Sadeq al-Ahmar are trying to make their way to his Sana'a neighborhood , which is being pounded by government forces. They say dozens of people have been killed in the fighting.

Flights were suspended at the Sana'a airport as the fighting intensified and moved closer.

In the southern city of Taiz, troops have fired on protesters who are calling for an end to the rule of President Ali Abdullah Saleh. At least 25 people have died in the violence in Taiz in the past few days.

Yemen's unrest has caused a number of countries to close or scale back their diplomatic missions. Kuwait said Wednesday it had evacuated its embassy staff, joining Italy, Qatar and Germany in suspending operations in Yemen. The U.S. last week moved most non-essential staff out of the country.